Browsing by Author "Dr. Mazhar Amjad Gilani"

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A Comparative Study of Different DFT Functionals on the Nonlinear Optical (NLO) Properties of Some NLO Prototypes
(Library Information Services COMSATS University Islamabad Lahore Campus, 2020-02-19) Alina Waheed; SP19-R06-018; Dr. Mazhar Amjad Gilani; LHR TP 6521
he present study spotlights the fundamental insights about four different classes of functionals and their efficacy to calculate the nonlinear optical (NLO) and linear properties. For this study, urea and (p-NA) para-nitroaniline molecules are used up as reference organic molecules. For comparative analysis, there is a dire need of such database to be utilized by the researchers. We have reported a range of functionals including hybrid (B3LYP, PBE1PBE, BHandHLYP), meta-hybrid (M06, M06-2X, M06-HF, M06-L), long-range corrected (CAM-B3LYP, LC-BLYP, LC-B97D, LCB97D3) along with dispersion correction (ωB97, ωB97X, ωB97XD, HSEH1PBE). These groups are evaluated and their efficiency to calculate linear and NLO properties is graphically compared with each other. NLO properties including anisotropic and linear isotropic polarizabilities, dipole moment, second- and third- order polarizabilities were analysed using their corresponding groups and there functionals. The presented results will help researchers to compare their calculations for the properties of NLO in different species. The current study highlights the importance of different functionals and their methods to be employed on various organic and inorganic species to study and evaluate their hyperpolarizabilities. The dipole moment of urea has been found to be 5.14 D which is close to experimentally determined value of 4.56 D. Similarly, the respective experimental and theoretical values of average second order polarizability as calculated by ωB97XD are quite close to each other. Interestingly, similar values of LC-B97D and LC-B97D3 for all the calculated parameters are obtained corresponding to urea and p-NA. A good agreement has been noticed among geometries, total electronic dipole moments and NLO polarizabilities on comparative basis. In addition, the (MEP) molecular electrostatic potential and (FMO) frontier molecular orbital map analyses are executed for the visual insight of charge transfer and predicting the reactive sites. In short, the current work provides significant methods to study the dipole moment, bond lengths, bond angles, static and frequency dependent second order and third-order polarizabilities. linear isotropic and anisotropic polarizabilities. Hence, the present results will attract the scientific community to compare their experimental work on various organic species with our results of urea and p-NA. These compounds are widely used as reference species in experimental and theoretical appraisal in the field x of nonlinear and linear optics. The current investigation will evoke scientific interest regarding the promising comparison of NLO properties in various organic species which can be beneficial in modern hi-tech applications.
A First Principle Study on Sensing Properties of Twisted Nanographenes Towards Phosgene, Thiophosgene and Formaldehyde
(Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-24) Naila Sattar; FA19-R06-007; Dr. Mazhar Amjad Gilani; LHR TP 7324
The harmful chemicals like chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) are extremely pernicious to the climate and living systems. The efficient detection and removal of these noxious chemicals in limited time span is essential for the human health and environmental security. Twisted nanographenes have great applications in the fields of energy storage and optoelectronics, but their applications as sensors are rarely described. Therefore, we have explored theoretically the sensitivity and selectivity of twisted nanographenes C32H16, C64H32 towards the harmful chemicals like phosgene, thiophosgene and formaldehyde. Here, we elaborate the phenomena of adsorption of the selected toxic chemicals on twisted nanographenes' surface within the framework of density functional theory (DFT). Adsorption interpretation is depending upon the optimized geometries, adsorption energies, NBO (natural bond orbital) charge transfer, frontier molecular orbital (FMO), absorption (UV-Vis), NCI (non-covalent interaction) and QTAIM (quantum theory of atoms in molecules) analyses. Results of interaction energies reveal the physiosorption of the toxic chemicals on the twisted nanographenes surface, which mainly arise due to the non-covalent interactions. The non-covalent nature of adsorption of toxic chemicals on twisted nanographenes surface is also ascribed by the NCI and QTAIM analyses. Most favorable adsorptions of the selected toxic chemicals occur at the edges of the distorted moiety (central ring). The average band gap changes (%Eg) and %sensitivity is quantitatively determined by the molecular orbital analysis, to evaluate the sensitivity of twisted nanographenes. Among the selected chemicals, the sensing of thiophosgene (ThP) is prominent on the twisted nanographenes surface, having interaction energies of -8.19 and -12.14 kcal mol-1 (in case of C32H16 and C64H32 tNGs), respectively. Therefore, it is concluded that twisted nanographenes can be applied as a potential sensing agent for the detection of toxic chemicals, especially thiophosgene. This x research will help the experimentalists to devise novel sensors based on twisted nanographenes.
A Theoretical Exploration of Supramolecular Architectures as High Performance Nonlinear Optical (NLO) Materials
(Library Information Services COMSATS University Islamabad Lahore Campus, 2022-02-26) FA20-R06-001; Aqsa Nisar; Dr. Mazhar Amjad Gilani; LHR TP 7876
Density functional theory (DFT) calculations have been performed for a series of supramolecular assemblies containing azobenzene (Azo-X where X=I, Br and H) and alkoxystilbazole subunits to evaluate their electronic, linear and nonlinear optical properties. These assemblies are derivatives of azobenzene, obtained by the substitution of electron-withdrawing and electron-donating groups onto the molecular skeleton. The interaction energies (Eint) of all the designed supramolecular complexes (IA-IF, IIA-IIF and IIIA-IIIF) range from -1.02 kcal/mol to -7.70 kcal/mol. Electronic properties of these hydrogen/halogen bond driven supramolecular assemblies such as, vertical ionization energies (VIE), HOMO-LUMO energy gap (GH-L), excitation energies, density of states (DOS) and natural bond orbital (NBO) analyses were also computed. The non-covalent interaction index (NCI) and quantum theory of atoms in molecules (QTAIM) analyses have also been performed to validate the nature of inter- and intra-molecular interactions in these complexes. A substantial enhancement in the first hyperpolarizability (βₒ) values of the designed supramolecular complexes has been observed driven by the charge transfer from the pyridyl moiety of alkoxystilbazole to Azo-X. The highest first hyperpolarizability (βₒ) value of 1.3×104 au is observed for supramolecular complex of p-nitro substituted azobenzene with alkoxystilbazole (ID complex). It was confirmed on a purely theoretical basis that both the type of noncovalent interactions present and the substituent group incorporated influence the nonlinear optical response (NLO) of the systems.
Bi-doping of Alkali Metals M2 (M2=Li2, Na2, and K2) on Al12N12 Nano-cage: A New Effective Approach to Design Nonlinear Optical Material
(library Information Services CUI Lahore Campus, 2020-02-16) Muhammad Sohail; FA18-R06-025; Dr. Mazhar Amjad Gilani; LHR TP 5966
Under the framework of density functional theory (DFT), M2@x-Al12N12 (M2=Li2, Na2, and K2; x=b66, Ntop, and r6) complexes have been designed. These highly stable complexes are formed through doping of bi-alkali metals at the surface of inorganic Al12N12 nano-cage. Both alkali metal atoms were doped in a trans-fashion over nitrogen atoms of Al12N12 (Ntop) or Al-N fused bond (b66) and over six-membered rings (r6). For the b66 and Ntop positions, the trend of stability for the complexes is Li2->Na2->K2-complexes. However, in cage doping position of r6, the stability is increased in the order of Li2->K2->Na2-complexes. The analysis of our computed data revealed that the large band-gap between HOMO (Highest occupied molecular orbital) and LUMO (Lowest unoccupied molecular orbital) of pure Al12N12 nano-cage can be decreased significantly within the range of 0.74-1.67 eV through doping of bi-alkali metals, thus showing the fascinating n-type behavior. A new HOMO orbital formed between the original band-gap of pure Al12N12 is responsible for the reduction in band gap. The doping of bi-alkali metals M2 on Al12N12 nano-cage results in a remarkable nonlinear optical response (β0). The calculated highest first hyperpolarizability values are 127397.94 au for K2@Ntop-Al12N12, 670.67 au for K2@r6-Al12N12, and 1028 au for Na2@b66-Al12N12 respectively. The hyperpolarizability values are increased with the increase in the atomic number of bi-alkali metals when bi-alkali metals are doped over Ntop and r6 positions. These intriguing results would be helpful to pursue future uses of modified doped Al12N12-based nano-cages in the latest kind of electronic and high efficient NLO (Nonlinear optical) nano-devices.
Covalent Organic Framework Supported Single Atom Catalyst for Hydrogen Evolution Reaction: A Theoretical Investigation
(Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-26) Maria Younas; SP20/R06/025; Dr. Mazhar Amjad Gilani; LHR TP 7579
Global environmental considerations are being raised as a result of excessive fossil fuel consumption and excessive carbon dioxide (CO2) emission. Regrettably, fossil fuel reserves are decreasing, and energy generation from them is unsustainable, non-renewable, and unaffordable. Due to these concerns, there is an imperative demand for sustainable and eco-friendly energy conversion electrochemical systems. Hydrogen (H2) is ubiquitously regarded as a future sustainable energy source and an attractive alternative to conventional fossil fuels. Production of hydrogen must be sustainable in order for a hydrogen economy to thrive in the future. Water electrolysis powered by renewable resources is being considered as a sustainable approach to produce hydrogen. In attempt to implement the process of water splitting efficiently, cost-effective, and non-precious metal based electrocatalysts for hydrogen evolution reaction (HER) are required. The development of effective single-atom catalysts (SACs) for electrochemical water splitting is a viable technique. High energy barrier of the HER and a catalyst with low stability continue to pose difficulties for the entire process of water splitting. To address this issue, electrocatalysts with single metal atoms supported on a covalent organic framework (TM@COF SACs) have been proposed for HER. The catalytic performance of these catalysts for HER is determined by the change in the Gibbs free energy of adsorbed atomic hydrogen (ΔGH*) on the catalyst's surface. Density functional theory (DFT) findings suggest that the Zn single atom doped on the surface of the covalent organic framework has a significant impact on the HER performance. This study paves the way for the development and use of highly efficient, stable, and non-precious single atom HER catalysts.
Density Functional Theory (DFT) Investigation of Electronic and Optical Properties of Azo Dyes
(Library Information Services COMSATS University Islamabad Lahore Campus, 2020-02-17) Muhammad Fahid Asif; FA18-R06-027; Dr. Mazhar Amjad Gilani; LHR TP 5968
Nonlinear optics is an important field of research owing to its extensive usage in advanced technologies. NLO materials have widespread applications in photonics and optoelectronics. NLO materials are crucial components of optical fibers, optical computing, data processing devices, optical sensors, optical modulators, high density optical storage devices, and ultra-fast optical switches. Five commercially available azo dyes, Acid Orange 5, Acid Orange 61, Direct Red 111, Food Yellow 6 and Metanil Yellow were theoretically investigated for their electronic and nonlinear optical properties using density functional theory (DFT) calculations. Each azo dye exhibits one alkaline and two acidic forms dominantly. So, all the three forms of these azo dyes were considered for calculations. Computational results reveal that these dyes possess high planarity across Ar-N=N-Ar’ linkage. Dihedral angles of alkaline and acidic I forms are found in range of 179o-179.9o. In acidic II forms, dihedral angles are distorted up to 176o owing to their geometrical change due to protonation. FMO analysis shows reduced HOMO-LUMO band gap for acidic forms as compared to alkaline forms. The drop in Eg values is attributed to the protonation which stabilizes the molecule by countering the excessive negative charge due to the sulphonic group. The HOMO-LUMO band gap lies in the range of 2-5 eV. The lowest HOMO-LUMO band gap of 2.54 eV is observed for AO61 AC I form. Low Eg values make azo dyes conductors. Furthermore, the effect of protonation of the dyes on nonlinear optical (NLO) responses was thoroughly investigated. Long range corrected method CAM-B3LYP/6-311-g(d) was employed for computation of polarizability and hyperpolarizability values. The results show that protonation of the dyes brings significant increase in nonlinear response. The highest first hyperpolarizability is observed for DR111 AC II (βo =2.6 x 104 au). TD-DFT calculations were also carried out to find change in dipole moment, crucial excited state energy difference and oscillator strength to estimate first hyperpolarizability using two-level-model. The βo (TLM) values calculated for dyes using two-level-model are comparable to the βo. It was also found that the change in dipole moments and change in excitation energies are the decisive factors for the increased first hyperpolarizabilities. In order to find the practical usability of the dyes in the field of nonlinear optics, FD-DFT calculations were performed at 532nm and 1064nm. The values of β (-2ω, ω, ω) and β (-ω, ω, 0) are estimated of the orders of 106 au and 105 au, respectively. The results are found to be quite supportive for application of the studied azo dyes in SHG phenomena.
Design of Novel Alkali Metals (Li, Na, K) Doped [6] Cycloparaphenylenes with High Nonlinear Optical Response
(Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-26) Ruqiya Rasul; SP20/R06/011; Dr. Mazhar Amjad Gilani; LHR TP 7565
Nonlinear optical (NLO) materials have gained tremendous attention because of their vast applications in different fields such as optoelectronics, telecommunication and data storage etc. In this work, geometric, electronic, linear and nonlinear optical properties of alkali metals (Li, Na and K) doped cyclic organic systems i.e., [6] cycloparaphenylene ([6]CPP) and methylene bridged [6] cycloparaphenylene (MB[6]CPP) are investigated via density functional theory (DFT). The diffuse excess electrons generated by alkali metals have significantly tuned their electro-optical properties. The alkali metals doped CPP based complexes have exhibited a large thermodynamic stability up to -32.1 kcal/mol. Moreover, reduction in HOMO-LUMO (H-L) energy gap has been observed up to 2.92 eV because of the generation of new HOMO which is further confirmed by density of state (DOS) analysis. The NBO analysis has revealed the charge transfer from metals to the CPPs. In addition, NCI and QTAIM analyses have exploited the nature of intramolecular interactions. Doping of alkali metal atoms significantly has increased the first hyperpolarizability (βₒ) of all the complexes. The K@r6-[6]CPP has exhibited the highest hyperpolarizability value of 1.10 x 107 au. Moreover, the absorption spectra have revealed the bathochromic shift for the alkali metals doped complexes. Furthermore, the frequency dependent first hyperpolarizability calculations have been done for M@r6 doped [6]CPP and MB[6]CPP at two routinely used frequencies (532 nm and 1064 nm). The results have shown that the highest response of both SHG (2.25 × 107 au) and EOPE (2.81 × 106 au) are obtained for K@r6-[6]CPP at 1064 nm. These fascinating results will be helpful to utilize the designed [6]CPP and MB[6]CPP based complexes for the generation of advanced optoelectronic devices and high performance NLO materials.
Design of Novel Lanthanum Doped Al12P12 Nanocages with High Nonlinear Optical Response
(Library Information Services COMSATS University Islamabad Lahore Campus, 2020-02-20) Faiqa Khaliq; SP19-R06-022; Dr. Mazhar Amjad Gilani; LHR TP 6523
In current study, the effect of lanthanum doping over Al12N12 and Al12P12 nanocages has been investigated using density functional theory. The strong influence of lanthanum doping on geometrical, electronic, linear, and nonlinear optical properties of Al12N12 and Al12P12 nanocages has been observed. The results revealed that doped nanoclusters possess high thermodynamic stability upto -37.37 kcal/mol and HOMO-LUMO gap is reduced upto 0.89 eV. NBO analysis confirms the charge transfer from metal towards nanocage. The Partial Density of States (PDOS) and Total Density of States (TDOS) strongly support the formation of new HOMO energy level which contributes in the reduction of HOMO-LUMO orbital energy gap. Doping of lanthanum remarkably increases the first hyperpolarizability (βₒ) of the complexes. The highest first hyperpolarizability of 4.43 × 104 au is observed for La@endo-Al12N12 complex. The present investigations intrigue the designing of high performance NLO materials that can be beneficial for their use in modern optoelectronic applications.
Detection of Histamine and Serotonin as Chronic Stress Biomarkers Using Graphyne-based Sensor: A DFT Study
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2025) Amina Haq; FA22-R06-027; Dr. Mazhar Amjad Gilani; LHR TP 9317
Chronic stress is a leading cause of mental illnesses that is interceded by neuroinflammation and poses one of the most critical public health challenges globally therefore, a theragnostic strategy is needed for effective diagnosis of stress. Neuroinflammation induces an increase in histamine and a decrease in serotonin levels in blood during chronic stress. The sensitivity of pristine and alkali metal (IA = Li, Na, and K) doped C24H12 toward histamine and serotonin are probed herein at DFT/ωB97XD/6 31+G (d, p) level of theory in the water phase. The -NH2 group of histamine and -OH group of serotonin are coordinated with pristine and metal-doped C24H12 nanosheets. The adsorption of histamine and serotonin is an exothermic process and physi-chemisorbed as their adsorption energies range from -40 to -60 kJ/mole per atom for all complexes except His@C24H12, His@KC24H12, and Ser@C24H12. Considerable, charge transfer from biomarkers to the C24H12 except for Ser@C24H12 is revealed via NBO analysis and confirmed by.MEP, UV-visible, and IR spectroscopic analyses. Upon the adsorption of the biomarkers, the λmax of pristine C24H12 remains unchanged but, in metal-doped C24H12, a bathochromic effect is observed. The significant shift in vibrational frequencies of -NH and -OH stretch occurred due to charge transfer toward C24H12. Furthermore, the band gap of the pristine C24H12 is 6.86 eV which remains constant even after histamine and serotonin adsorption. However, the doping of alkali metals leads toward a significant decrease of the band gap of about 4.60 eV revealing that doping facilitated the charge transfer from biomarkers to graphyne for effective sensing. The QTAIM and IRI studies show the presence of non-covalent interactions among the biomarkers and C24H12. Finally, a shorter recovery time (fast desorption) is found in vacuum ultraviolet light, indicating the pristine and metal-doped C24H12 nanosheets as a reusable or non-disposable sensor. Therefore, it concludes that metal-doped C24H12 nanosheets are more sensitive toward histamine and serotonin adsorption than pristine C24H12.
Effect of Electric Field Variation on Electronic and Nonlinear Optical (NLO) Properties of Ionic Liquids: A DFT Study
(Library Information Services COMSATS University Islamabad Lahore Campus, 2023-02-27) Dua Fatima; SP22-R06-018; Dr. Mazhar Amjad Gilani; LHR TP 8657
The growing use of nonlinear optical (NLO) materials in various fields has generated interest in designing innovative smart NLO materials. This study focuses on three specific ionic liquids, where the same cation, 1-ethyl-3-methyl imidazolium, is combined with three different anions (Br-, C-, F-). The study explores the effects of External Electric Field (EEFs) on these three ILs using Density Functional Theory (DFT) calculations. The interaction energies calculated confirm the stability of the newly designed ILs. Applying external electric field (EEFs) ranging from 0.001 a.u to 0.006 a.u leads to a significant reduction in the E(H–L) gap, and the lowest energy gap of 4.43 eV is observed in EMIBr at field strength of 0.006 a.u. Natural Bond Orbital (NBO) analysis validates substantial charge transfer from cations to anions, with the highest transfer observed in EMIBr. External Electric field enhances the first hyperpolarizability, and EMIBr exhibits the highest value i.e 1828 a.u at 0.006 a.u. TD-DFT calculations are executed to derive electronic states influenced by an external electric field (EEF), and the highest λmax (nm) i.e. 227 nm, is observed in the case of EMIBr at 0.006 a.u. The study also determines frequency-dependent Second Harmonic Generation (SHG) and Electric-Optical Pockels Effect (EOPE), with noteworthy values observed i.e 2.0×103 and 9.8×103 respectively in case of EMIBr. In conclusion, the study provides guidelines for computationally designing efficient and thermodynamically stable complexes for optical and optoelectronic technologies. The proposed ILs could find potential applications in new electronic devices, contributing to the development of advanced NLO materials.
Exploration of Diradical Graphene Nanoflakes (GNFs) as NLO based Sensors for NOx
(Library Information Services COMSATS University Islamabad Lahore Campus, 2023-02-27) Mawra Nasir; SP22-R06-009; Dr. Mazhar Amjad Gilani; LHR TP 8648
Approximately 78% of the air is composed of nitrogen, which, in its elemental form, is not harmful. However, nitrogen oxides (NO, NO2, N2O) present in the air can have adverse effects on both human health and the environment. In the realm of environmental monitoring, the crucial task of adsorbing or detecting small (toxic) gas molecules relies on appropriate semiconductors. Although graphene nanoflakes (GNFs) find extensive applications in energy storage and optoelectronics, their potential as sensors is not extensively explored. This study investigates the adsorption of nitrogen-containing gaseous molecules i.e NO, NO2, and N2O on trigonal, rhombic, and bowtie GNFs sheets through Density Functional Theory (DFT) simulations. The analysis encompasses optimized geometries, adsorption energies, as well as Natural Bond Orbital (NBO) and Electron Density Differences (EDD) analyses to interpret the interaction between GNFs sheets and NOx gases. The theoretical findings reveal strong binding between GNFs sheets and NO2 molecule, with adsorption energies of -30.2, - 17.1, and -29.8 kcalmol-1 for NO2@t-GNFs, NO2@r-GNFs, and NO2@b-GNFs, respectively. Furthermore, Frontier Molecular Orbital (FMO), and Density of State (DOS) analyses underscore the significant impact of gas adsorption on GNF sheets. Interaction Region Indicator (IRI) and Quantum Theory of Atoms in Molecules (QTAIM) analyses indicate the covalent interactions between GNFs sheets and NO, NO2 gases, while van der Waals interactions are confirmed with N2O gases. UV-Vis and IR analyses demonstrate the selectivity of b-GNFs towards NO2 and NO, respectively. Based on Nonlinear Optical (NLO) response, b-GNFs exhibit the highest sensitivity towards NOx. In conclusion, GNFs sheets exhibit promising sensitivity to gaseous molecules, positioning them as potential multimode sensors, including UV, IR, and NLO-based applications. This theoretical insight aids experimentalists in developing novel GNFs-based sensors for the detection of toxic gases.
Hydrogen Adsorption and Dissociation Using Single Metal Atom Doped Mg12O12 Nanocage as a Catalyst: A DFT Study
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2025) Irsa Nageen; FA22-R06-008; Dr. Mazhar Amjad Gilani; LHR TP 9309
Energy is the keystone of life on Earth, powering everything from microscopic levels to large scale chemical reactions. The expanding population and increasing industrial activities have reinforced the energy demands, traditionally sourced from fossil fuels. However, the finite nature of these resources and their detrimental environmental impacts necessitate a transition to sustainable energy solutions. Currently, hydrogen emerges as the outstanding substitute for fossil fuels, making it a more valuable energy source due to its high energy density, renewability, and clean burning nature, producing only water as a by-product. Hence, efficient hydrogen utilization requires its dissociation because molecular hydrogen is not an effective energy source as the atomic form. In this regard, hydrogen dissociation reaction on single-atom catalysts (SAC) is an essential step in sustainable and non-toxic energy production. Our study employed DFT calculations to investigate the adsorption and dissociation of molecular hydrogen on 3d transition metal atoms doped onto Mg12O12 nanocages. Each TM@Mg12O12 complex is evaluated to identify the most stable spin state for the catalytic reaction. The energetic analysis reveals that the Sc@Mg12O12 and Ti@Mg12O12 complexes exhibit high and identical interaction energy (-2.13eV) among the studied complexes. Further evaluation using NBO, FMO, IRI, and QTAIM analysis revealed the charge transfer carried from nanocage to metal and confirmed the partial covalent interactions between the TM-doped complexes. The adsorption of molecular hydrogen on the TM-doped nanocage exhibits negative adsorption energy which confirms the exothermic nature of H2 adsorption. Notably, the homolytic dissociation of H2 on the Ti@Mg12O12 complex displayed the lowest activation barrier (0.23eV), highlighting its potential as an efficient catalyst for hydrogen dissociation reactions. QTAIM of H2TM@Mg12O12 studies the interaction between the hydrogen and catalyst and confirms the covalency. NBO and EDD analysis confirm the transfer of charge from metal bonding to hydrogen antibonding orbital which leads to the dissociation of the H-H bond and facilitates the adsorption of hydrogen atoms on the catalyst. Our investigation sheds light on the factors that govern the electronic properties and catalytic ability of TM-doped Mg12O12 nanocage complexes in hydrogen dissociation reactions and paving the way for the development of improved hydrogen energy technology.
Hydrogen Splitting using Single Metal Atom Doped Zinc Oxide Nanocage as a Catalyst: A DFT Study
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2023) Ali Hussain; FA21-R06-016; LHR TP 8447; Dr. Mazhar Amjad Gilani
Hydrogen dissociation reaction is a key step in sustainable, non-toxic and renewable energy production and single atom catalysts have shown promising catalytic activity in facilitating this reaction. The world is currently facing major challenges related to the environment, including climate change and the depletion of non-renewable energy sources. As a potential solution to these challenges, the use of clean and renewable energy sources, such as hydrogen, has gained increasing attention. Herein we employed DFT calculation on single atom catalyst-based study to investigate the adsorption and dissociation of H2 molecule over TM@ Zn12O12 catalysts. The analysis of the interaction energy reveals the stability of all transition metal doped complexes (Sc-Mn), with the highest interaction energy (-4.27 eV) observed in the Cr@Zn12O12 complex. Furthermore, electronic properties (FMOs, NBO analysis) confirm the electropositive nature of transition metal atoms. QTAIM and IRI analysis are employed to interpret shared or partially covalent interactions in TM@ Zn12O12 complexes. The mechanism of hydrogen dissociation reaction is studied for all the complexes (Sc-Mn), and it is found that Sc@Zn12O12 is the most efficient catalytic agent for the hydrogen dissociation reaction, with the lowest activation barrier (0.09 eV). EDD isosurface and NBO analysis confirm the charge transfer from metal to antibonding orbital of hydrogen which facilitates the hydrogen splitting. The pivotal insights gained from this study enhance our understanding about the stability, electronic properties, and hydrogen dissociation reaction of various transition metal doped Zn12O12complexes.
Hydrogen Splitting Using Single Metal Atom Doped C3N Nanosheet as a Catalyst: A DFT Study
(Library Information Services COMSATS University Islamabad Lahore Campus, 2022-02-26) Zulqarnain Haider; FA20-R06-010; Dr. Mazhar Amjad Gilani; LHR TP 7881
Atomic hydrogen is the most intriguing free radical for high-energy applications. The ability of atomic hydrogen to protect DNA and mitochondria from oxidative damage may be advantageous in the treatment of chronic illnesses including cancer. When dissociation energy is supplied, a molecule of hydrogen dissociates into two atoms (H2 → 2H). In contrast to other radicals, hydrogen recombination requires no activation energy. The highest efficiency and stability for heterogeneous catalysis of hydrogen splitting are provided by single-atom catalysts adsorbed on the active surface. For support of single-atom catalyst (SAC), carbon nanotubes, graphene, metal hydrides, metal-organic frameworks, graphene, graphdiyne, carbon nitride, and silanes surfaces have been employed recently. The presence of nitrogen in carbon nitride surfaces is shown to be much more effective for hydrogen dissociation and considered as the most suitable substrate for SAC. Because of their varying oxidation states, transition metals have several spin states that can be tested, and the most stable spin states based on thermodynamic energy data may be determined. The optimized C3N nanosheet is doped with 3d transition metals. The lowest energy spin state of each doped metal is considered for further calculations. The stabilities of complexes have been measured by calculating the interaction energies of optimized geometries. Adsorption energies of H2 on metal doped carbon nitride surface are computed to investigate the adsorption mechanism and characterize the energetic heterogeneity of solid surfaces. The energy barrier (activation energy) and reaction energies are required to determine the splitting of hydrogen. This study shows that SAC can be used as the most efficient doping technique for hydrogen splitting.
Hydrogen Splitting using Single Metal Atom Doped Zinc Oxide Nanocage as a Catalyst: A DFT Study
(Library Information Services COMSATS University Islamabad Lahore Campus, 2023-02-26) Ali Hussain; FA21-R06-016; Dr. Mazhar Amjad Gilani; LHR TP 8447
Hydrogen dissociation reaction is a key step in sustainable, non-toxic and renewable energy production and single atom catalysts have shown promising catalytic activity in facilitating this reaction. The world is currently facing major challenges related to the environment, including climate change and the depletion of non-renewable energy sources. As a potential solution to these challenges, the use of clean and renewable energy sources, such as hydrogen, has gained increasing attention. Herein we employed DFT calculation on single atom catalyst-based study to investigate the adsorption and dissociation of H2 molecule over TM@ Zn12O12 catalysts. The analysis of the interaction energy reveals the stability of all transition metal doped complexes (Sc-Mn), with the highest interaction energy (-4.27 eV) observed in the Cr@Zn12O12 complex. Furthermore, electronic properties (FMOs, NBO analysis) confirm the electropositive nature of transition metal atoms. QTAIM and IRI analysis are employed to interpret shared or partially covalent interactions in TM@ Zn12O12 complexes. The mechanism of hydrogen dissociation reaction is studied for all the complexes (Sc-Mn), and it is found that Sc@Zn12O12 is the most efficient catalytic agent for the hydrogen dissociation reaction, with the lowest activation barrier (0.09 eV). EDD isosurface and NBO analysis confirm the charge transfer from metal to antibonding orbital of hydrogen which facilitates the hydrogen splitting. The pivotal insights gained from this study enhance our understanding about the stability, electronic properties, and hydrogen dissociation reaction of various transition metal doped Zn12O12complexes.
Substitution of Alkali Metal Atoms: An Efficient Approach to Enhance Electronic and Nonlinear Optical Properties of Diamantane
(library Information Services CUI Lahore Campus, 2020-02-16) Palwasha Khan; SP19-R06-012; Dr. Mazhar Amjad Gilani; LHR TP 6515
Applications of nonlinear (NLO) materials in the fields like electronics, optics, optoelectronics, and optical computing, etc. drive the interest of many scientists to design high-performance NLO materials. Electronic properties, absorption spectra and nonlinear optical properties of alkali metal substituted diamantanes are presented. A significant reduction in HOMO-LUMO gap has been observed by alkali metal substitution. K@CHa has the lowest H-L gap of 1.64 eV as compared to 8.88 eV for pristine diamantane. A remarkable increase in the first hyperpolarizability (βₒ) has been observed due to the substitution of alkali metals. Among these structures, K substituted complexes show the largest first hyperpolarizability (25526-36328 a.u). This significant increase in the first hyperpolarizability (βₒ) is attributed to low crucial transition energies ΔE. K@CHa has the lowest ΔE value (2.0650 eV) which results in the highest βₒ value (36328 a.u.) for K@CHa. Furthermore, frequency-dependent hyperpolarizabilities calculations are carried out using 1906 nm, 1340 nm, and 1064 nm frequencies for commonly used lasers. This study provides an efficient approach to design high-performance NLO materials having extensive applications in the field of electronics and optoelectronics. The results reveal that substitution of alkali metals leads to the shift in absorption from ultraviolet to the visible
Theoretical Assessment of Corannulene-Based Aggregates as High-Performance Nonlinear Optical Materials
(Library Information Services COMSATS University Islamabad Lahore Campus, 2023-02-27) Sobia Waheed; SP22-R06-024; Dr. Mazhar Amjad Gilani; LHR TP 8662
The growing use of nonlinear optical (NLO) materials in various fields has generated interest in designing innovative smart NLO materials. This study focuses on enhancing the nonlinear optical response through doping of alkali metals on the corannulene (C20H10) dimer through Density Functional Theory (DFT) calculations. The interaction energies calculated computationally confirm the stability of the newly designed alkali metal-doped cncx dimers. Alkali metal doping, particularly with Li, Na, and K, leads to a significant reduction in the E(H–L) gap, and the lowest energy gap of 3.17 eV is observed in K-doped cncx dimer. The TD-DFT study shows that these alkali metal doped complexes have λmax in the visible regions(568-576nm). Total density of states (TDOS) spectra support the involvement of dimer in forming new Highest Occupied Molecular Orbital (HOMO). Natural Bond Orbital (NBO) analysis validates substantial charge transfer from alkali metals to dimer, with the highest charge transfer (0.938 |e|) observed in the K@cncx complex. Doping with alkali metals enhances the first hyperpolarizability, and Li@cncx exhibits the highest value (9.3×104 au). The study also determines frequency-dependent Second Harmonic Generation (SHG), Electric-Optical Pockels Effect (EOPE), electro-optic dc-Kerr effect (EOKE). The value of 3.4×104 au is observed for SHG, while for EOPE the value is 4.6×105 au. A significantly enhanced EOKE value (1.0 × 1010 au) is shown by Na@cncx. Additionally, these structures exhibit a high nonlinear quadratic refractive index (a maximum value of 9.9×10-18cm2 W-1). In conclusion, the study provides guidelines for computationally designing efficient and thermodynamically stable complexes for optical and optoelectronic technologies.
Theoretical Design of Alkali and Alkaline Earth Metals Doped Cubanes (C8H8) as Novel Nonlinear Optical Materials
(Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-25) Javaria Naeem; SP20/R06/013; Dr. Mazhar Amjad Gilani; LHR TP 7567
Novel organic materials have spark the attention of many scientists to design the high performance NLO materials. In the current study, the effect of alkali and alkaline earth metals doped cubanes have been studied by using density functional theory. The strong influence of doped metal atoms on structural, electronic and nonlinear optical prosperities have been investigated. The results have revealed thermodynamic stability of the doped complexes. The HOMO-LUMO energy gap is reduced upto 4.43 eV. Density of state analysis confirmed the formation of new highest occupied molecular orbital that contributes in the reduction of energy gap. The NBO analysis is performed to evaluate the charge transfer between metal atoms and the cubane ring. The NCI and QTAIM studies also validated the nature of the intramolecular interaction. Doping of metal atoms significantly boosts the hyperpolarizability of the complexes. The first hyperpolarizability (βₒ) of 3.01×104 au is observed for K@Cubane. Moreover, second hyperpolarizability (γtot), second harmonic generation (SHG), electro-optic Pockel’s effect (EOPE), electric field-induced second harmonic generation (EFISHG), electro-optic Kerr effect (EOKE), hyper-Rayleigh scattering coefficient (βHRS) and nonlinear refractive indices (n2) are also calculated for the designed complexes. The highest dc-Kerr of 2.03 × 1011 au and EFISHG of 2.06 × 1012 au are observed at ω= 0.0856 au along with large refractive index (1.15 × 10-5 au ). These remarkable findings offer new perspectives for designing new materials for their future applications in optoelectronics.
Theoretical Prediction of Nocturnal/Diurnal and Seasonal Real World Absorption Spectra of Polycyclic Aromatic Hydrocarbons and their Derivatives in Two Chinese Polluted Cities
(Library Information Services COMSATS University Islamabad Lahore Campus, 2021-02-24) Sahiba Fareed; FA19-R06-014; Dr. Mazhar Amjad Gilani; LHR TP 7320
Brown carbon (BrC) is an organic aerosol, released during combustion of organic matter. It strongly absorbs solar radiations hence, plays an important role in radiative forcing. Neglecting brown carbon from climate models leads to difference between theoretical and experimental works. Polycyclic aromatic hydrocarbons (PAHs) and their derivatives such as oxygenated polycyclic aromatic hydrocarbons (OPAHs) and nitrated polycyclic aromatic hydrocarbons (NPAHs) are the major constituents of the BrC and they are persistent environmental pollutants. Their study is the need of hour as they are ubiquitous in atmosphere and carcinogenic in nature. Our strategy here is to utilize time dependent-density functional theory (TD-DFT) to model the absorption spectra of PAHs and their derivatives in two Chinese industrial sites: Qingcheng district (site A) and Longtang town of Qingyuan (site B). These data are corrected for “Real-world” experimental concentrations of PAHs over these cities. For the first time, nocturnal/diurnal and seasonal variations of PAHs are being studied at a time in these Chinese regions. These findings show that most relevant absorption regions for climate forcing are ~320nm, ~380nm and ~430nm. Moreover, almost all the absorption at site A and B takes place mainly due to PAHs while OPAHs and NPAHs play a very negligible part in absorption. Site A is highly affected by climate forcing caused by these PAHs. Absorption in winter is higher as compared to that of in summer. Furthermore, this model infers that relevant contributors to absorption at ~320nm are PAHs and OPAHs while absorption at ~380nm is attributed only to PAHs. Absorption at ~430nm is mainly explained by PAHs and NPAHs. Most of the absorption takes place in UVA and visible regions of the electromagnetic spectrum. More specifically, from the 35 studied PAHs and their derivatives, the major contributors towards radiative forcing are DBA (dibenzo[ah]anthracene), BaA (benz[a]anthracene) and BkF (benzo[k]fluoranthene) (PAHs). While among OPAHs and NPAHs, major contributors are Bpone (6H-benzo[c,d]pyrene-6-one), Bzdion (Benzo[a]anthracene-7,12-dione) and 7NBaA (7-nitrobenz[a]anthracene). Thus, our x theoretical modeling approach remarkably identifies the most relevant PAHs, OPAHs and NPAHs for climate forcing in this Chinese region.
Theoretical Studies of Superalkalis Doping on Calix[4]arene; A Unique Approach for the Improvement of Nonlinear Optical Response
(Library Information Services COMSATS University Islamabad Lahore Campus, 2023-02-27) Khalida Khalil; FA21-R06-024; Dr. Mazhar Amjad Gilani; LHR TP 8454
Many scientists are interested in developing high-performance nonlinear materials because of their potential uses in areas such as optics, optoelectronics, optical computing, and others. Density Functional theory (DFT) is used to predict NLO response of the selected systems. The study revealed that the doping of superalkalis on calix[4]arene is an efficient strategy to design high performance NLO materials. The interaction energy (Eint) calculations are used to analyze the thermal stability of the complexes under consideration. Superalkali doping generates diffuse surplus electrons, which produce the alkalide properties in the corresponding systems. Through static and dynamic hyperpolarizability investigations, these alkalides are further studied for their nonlinear optical (NLO) responses. The large values of second (5.9×105) and third-order (1.9×108) NLO responses at 1200 nm, along with a high refractive index, demonstrate that the NLO response of the corresponding complexes increases at large wavelength. The nature of charge transfer was confirmed by the NBO analysis. The weak electrostatic interactions between calix[4]arene and superalkali was revealed through QTAIM and interaction region indicator analysis (IRI). The TD-DFT calculations confirmed the transparency of these superalkali (Li3O, Na3O and K3O) doped complexes in UV-VISIBLE regions. Overall, the study highlights the M3O@calix[4]arene as potential candidate for designing high performance NLO materials.