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Vikas - One of the best experts on this subject based on the ideXlab platform.
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Current‐Density functional study of the HeH+ molecular ion under a strong ultrashort magnetic field
International Journal of Quantum Chemistry, 2012Co-Authors: VikasAbstract:The HeH+ molecular ion under an ultrashort magnetic field on the order of 109 G is investigated through quantum fluid dynamics and a current-Density functional theory (CDFT) based approach, employing a vector exchange–correlation (XC) potential which depends on the Electronic Charge-Density as well as on the current-Density. The behavior of the exchange and correlation energies of the HeH+ ion is analyzed and compared with those obtained using an approach based on the time-dependent Density functional theory (TD-DFT) under similar computational constraints but employing a scalar XC potential dependent only on the Electronic Charge-Density. The CDFT-based approach yields exchange and correlation energies as well as TD Electronic Charge-densities drastically different from those obtained using the TD-DFT-based approach particularly, at typical TD magnetic field strengths. This is attributed to the nonadiabatic effects induced by the vector XC potential of the CDFT in the oscillating Charge-Density of the HeH+ ion, which are further explained in the terminology of quantum fluid dynamics. The vector XC potential of the CDFT-based approach is observed to augment the magnetic interactions in the H2 molecule and in the He ion, whereas it opposes the magnetic interactions in the HeH+ ion particularly, at the intermediate magnetic field strengths. © 2012 Wiley Periodicals, Inc.
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Current-Density functional theory study of the H2 molecule evolving under a strong ultrashort magnetic field
The European Physical Journal D, 2012Co-Authors: VikasAbstract:Hydrogen molecule in a strong ultrashort magnetic field is investigated through a current-Density functional theory (CDFT) and quantum fluid dynamics (QFD) based approach employing current-Density dependent vector exchange-correlation potential and energy Density functional derived with a vorticity variable. The numerical computations through the CDFT based approach are performed for the H2 molecule, starting initially from its field-free ground state, in a parallel internuclear axis and magnetic field-axis configuration with the internuclear separation R ranging from 0.1 a.u. to 14.0 a.u., and the strength of the time-dependent (TD) magnetic field varying between 0−1011 G over a few femtoseconds. The numerical results are compared with that obtained using an approach based on the current-Density independent approximation under similar computational constraints but employing only scalar exchange-correlation potential dependent on the Electronic Charge-Density alone. The current-Density based approach yields exchange- and correlation energy as well as Electronic Charge-Density of the H2 molecule drastically different from that obtained using current-independent approach, in particular, at TD magnetic field-strengths >109 G during a typical time-period of the field when the magnetic-field had attained maximum applied field-strength and is switched to a decreasing ramp function. This nonadiabatic behavior of the TD Electronic Charge-Density is traced to the TD vorticity-dependent vector exchange-correlation potential of the CDFT based approach. The interesting electron dynamics of the H2 molecule in strong TD magnetic field is further elucidated by treating Electronic Charge-Density as an ‘electron-fluid’. The present work also reveals interesting real-time dynamics on the attosecond time-scale in the Electronic Charge-Density distribution of the hydrogen molecule.
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He 2++ molecular ion in a strong time-dependent magnetic field: a current-Density functional study.
Journal of Computational Chemistry, 2011Co-Authors: VikasAbstract:The He molecular ion exposed to a strong ultrashort time-dependent (TD) magnetic field of the order of 109 G is investigated through a quantum fluid dynamics (QFD) and current-Density functional theory (CDFT) based approach using vector exchange-correlation (XC) potential and energy Density functional that depend not only on the Electronic Charge-Density but also on the current Density. The TD-QFD-CDFT computations are performed in a parallel internuclear-axis and magnetic field-axis configuration at the field-free equilibrium internuclear separation R = 1.3 au with the field-strength varying between 0 and 1011 G. The TD behavior of the exchange- and correlation energy of the He is analyzed and compared with that obtained using a [B-TD-QFD-Density functional theory (DFT)] approach based on the conventional TD-DFT under similar computational constraints but using only scalar XC potential and energy Density functional dependent on the Electronic Charge-Density alone. The CDFT based approach yields TD exchange- and correlation energy and TD Electronic Charge-Density significantly different from that obtained using the conventional TD-DFT based approach, particularly, at typical magnetic field strengths and during a typical time period of the TD field. This peculiar behavior of the CDFT-based approach is traced to the TD current-Density dependent vector XC potential, which can induce nonadiabatic effects causing retardation of the oscillating Electronic Charge Density. Such dissipative electron dynamics of the He molecular ion is elucidated by treating Electronic Charge Density as an electron-“fluid” in the terminology of QFD. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011
Sikander Azam - One of the best experts on this subject based on the ideXlab platform.
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Electronic Structure, Electronic Charge Density and Optical Properties Analyses of Rb 2 Al 2 B 2 O 7 Compound: DFT Calculation
2014Co-Authors: Ali H. Reshak, Zeyad A. Alahmed, Sikander Azam, Saudi ArabiaAbstract:We have presented an analysis of some important Electronic and optical characteristics of the Rb2Al2B2O7 compound, based on the ab initio calculations of its Electronic band structure, Electronic Charge Density and dielectric tensor function. The band gap is found to be indirect of about 4.156, 4.471 and 5.205 eV for LDA, GGA and EVGGA respectively. The contributions to the top of valence band and bottom of conduction band come predominantly from O s/p, Al s/p and Rb s/p states, respectively. The distribution of the total Electronic Charge Density maps (in the units of e/a.u. 3 ) has been calculated along the (101) plane. The optical absorption spectrum is calculated and interpreted in terms of Electronic band structure for incident radiation energy up to 14 eV. The principal absorption occurs within the energy range from 6.0 to 14.0 eV, originating mainly from the Electronic transitions from the O-s to Al-s/p states. The complex dielectric function, refractive index, birefringence, energyloss spectrum and reflectivity have been calculated.
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First principle study of the Electronic structure, Fermi surface, Electronic Charge Density and optical properties of ThCu5In and ThCu5Sn single crystals
Journal of Magnetism and Magnetic Materials, 2014Co-Authors: Ali H. Reshak, Sikander AzamAbstract:Abstract The Electronic structure, Fermi surface, Electronic Charge Density and optical properties of ThCu 5 In and ThCu 5 Sn single crystals are studied. The calculations are based on the full potential-linearized augmented plane wave (FPLAPW) method. The exchange and correlation potential is treated by the local Density approximation (LDA) and generalized-gradient approximation (GGA), in addition the Engel–Vosko (EV-GGA) formalism was also applied. The DFT calculations show that these compounds have metallic origin. The contribution of different bands was analyzed from total and partial Density of states curves. The values of the Density of states at Fermi energy ( N ( E F )) for ThCu 5 In (ThCu 5 Sn) is 1.75 (1.63) states/eV unit cell. The bare Electronic specific heat coefficient ( γ ) is found to be equal to 0.30 and 0.28 mJ/mol-K 2 for ThCu 5 In and ThCu 5 Sn, respectively. The Fermi surface of ThCu 5 In/ThCu 5 Sn is composed of three/four bands crossing along the R – Γ direction. The bonding features are analyzed by using the Electronic Charge Density contour in the (101) crystallographic plane and it shows the covalent character of Cu–Cu and Sn/In–Cu bonds. The optical properties were also calculated and analyzed.
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The Electronic structure, Electronic Charge Density and optical properties of the diamond-like semiconductor Ag2ZnSiS4
Applied Physics A, 2013Co-Authors: Ali H. Reshak, Sikander AzamAbstract:The Electronic structure, Electronic Charge Density and optical properties of the diamond-like semiconductor Ag2ZnSiS4 compound with the monoclinic structure have been investigated using a full-relativistic version of the full-potential augmented plane-wave method based on the Density functional theory, within local Density approximation (LDA), generalized gradient approximation (GGA), Engel–Vosko GGA (EVGGA) and modified Becke Johnson (mBJ) potential. Band structures divulge that this compound is a direct energy band gap semiconductor. The obtained energy band gap value using mBJ is larger than those obtained within LDA, GGA and EVGGA. There is a strong hybridization between Si-s and S-s/p, Si-p and Zn-s, Ag-s/p and Zn-s, and Ag-s and Ag-p states. The analysis of the site and momentum-projected densities shows that the bonding possesses covalent nature. The dielectric optical properties were also calculated and discussed in detail.
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first principles study of the Electronic structure Charge Density fermi surface and optical properties of zintl phases compounds sr2zna2 a p as and sb
Journal of Magnetism and Magnetic Materials, 2013Co-Authors: A H Reshak, Sikander AzamAbstract:Abstract We present first-principles calculations of the Electronic structure, Fermi surface, Electronic Charge Density and optical properties of Sr2ZnA2 (A=P, As and Sb) based on Density-functional theory using the local Density approximation (LDA), generalized-gradient approximation (GGA) and the Engel–Vosko GGA formalism (EV-GGA). Additionally, modified Becke–Johnson (mBJ) is also used to improve the band splitting results. The calculated band structure and Density of states show that Sr2ZnA2 compounds are metallic. The total DOS at Fermi level N(EF) is 72.92, 73.06 and 33.47 states/eV and the bare Electronic specific heat coefficient (γ) is 12.64, 5.805 and 12.67 mJ/mol-K2 for Sr2ZnP2, Sr2ZnAs2 and Sr2ZnSb2, respectively. The Fermi surface of Sr2ZnA2 compounds is composed of two bands crossing along the Γ−A direction of Brillouin zone. There exists a strong hybridization between Zn-p/s and Sb-d, Sb-p and Sr-d and also between Sr-s and Sr-p states. The bonding features are analyzed by using the Electronic Charge Density contour in the (101) crystallographic plane. We found that Sr forms an ionic bond with Zn, whereas Zn forms a strong covalent interaction with P/As/Sb atoms. For further insight information about the Electronic structure, the optical properties are derived and analyzed.
A H Reshak - One of the best experts on this subject based on the ideXlab platform.
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linear nonlinear optical susceptibilities hyperpolarizability and space Electronic Charge Density of meso silver i histidinate ag d his n hhis histidine
Polyhedron, 2015Co-Authors: Saleem Ayaz Khan, A H ReshakAbstract:Abstract Full potential linear augmented plane wave method was used to calculate the Electronic band structure, Density of states, Charge Density and optical properties of meso silver(I) histidinate [Ag(D-his)]n. The band structure investigation elucidated that the investigated compound possess indirect (Z → Γ) broad gap. The effective mass ratio for electron, light hole and heavy hole were calculated in conduction band minimum (0.0596), upper valence band maximum (0.5085) and lower valence band maximum (0.3612) respectively. The total valence Charge Density shows covalent nature of [Ag(D-his)]n bonds. The compound contains two heterodimers per unit cell. The calculated length of the O–H bond that formed heterodimer is 1.67 A. The average value of real and imaginary part of dielectric function were calculated. The three principal tensor components of ɛ2(ω), ɛ1(ω), n(ω), I(ω) and R(ω) were calculated and discussed in detail. The calculated uniaxial anisotropic value (0.0985) and birefringence (0.06) has indicated the strong anisotropy of the dielectric function in [Ag(D-his)]n. The investigation of n(ω) spectra shows the superluminality in ultraviolet region while R(ω) spectra shows that [Ag(D-his)]n is suitable for antireflection coating material for solar cells in infrared and visible region. The investigated compound also exhibit second harmonic generation of about 1.57 pm/V at static limit and 2.34 pm/V at λ = 1064 nm. We have also calculated the microscopic first hyperpolarizability β213(ω) for the dominant component χ 213 ( 2 ) ( ω ) at static limit 0.666 × 10−30 esu and at λ = 1064 nm (0.965 × 10−30 esu).
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first principles study of the Electronic structure Charge Density fermi surface and optical properties of zintl phases compounds sr2zna2 a p as and sb
Journal of Magnetism and Magnetic Materials, 2013Co-Authors: A H Reshak, Sikander AzamAbstract:Abstract We present first-principles calculations of the Electronic structure, Fermi surface, Electronic Charge Density and optical properties of Sr2ZnA2 (A=P, As and Sb) based on Density-functional theory using the local Density approximation (LDA), generalized-gradient approximation (GGA) and the Engel–Vosko GGA formalism (EV-GGA). Additionally, modified Becke–Johnson (mBJ) is also used to improve the band splitting results. The calculated band structure and Density of states show that Sr2ZnA2 compounds are metallic. The total DOS at Fermi level N(EF) is 72.92, 73.06 and 33.47 states/eV and the bare Electronic specific heat coefficient (γ) is 12.64, 5.805 and 12.67 mJ/mol-K2 for Sr2ZnP2, Sr2ZnAs2 and Sr2ZnSb2, respectively. The Fermi surface of Sr2ZnA2 compounds is composed of two bands crossing along the Γ−A direction of Brillouin zone. There exists a strong hybridization between Zn-p/s and Sb-d, Sb-p and Sr-d and also between Sr-s and Sr-p states. The bonding features are analyzed by using the Electronic Charge Density contour in the (101) crystallographic plane. We found that Sr forms an ionic bond with Zn, whereas Zn forms a strong covalent interaction with P/As/Sb atoms. For further insight information about the Electronic structure, the optical properties are derived and analyzed.
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Electronic structure, Density of Electronic states, and the chemical bonding properties of 2,4-dihydroxyl hydrazone crystals (C_13H_11N_3O_4)
Journal of Materials Science, 2013Co-Authors: A H Reshak, H. Kamarudin, S. AuluckAbstract:Electronic crystal structure, bonding properties, and the electron Charge densities of 2,4-dihydroxybenzaldehyde-4-nitrophenylhydrazone (2,4-DHNPH,C_13H_11N_3O_4) crystal are theoretically investigated. Calculations are performed with local Density approximation, generalized gradient approximation, the Engel–Vosko generalized gradient approximation, and modified Becke–Johnson potential. We present the results of the total and partial (C, N, O, H atoms) Density of states. Furthermore, the Electronic Charge Density space distribution contours in the (1 1 0) crystallographic plane, which gives better insight picture of chemical bonding were calculated to understand the effect of hydrogen bonding on the crystal structure of 2,4-DHNP.
Yosslen Aray - One of the best experts on this subject based on the ideXlab platform.
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C library for topological study of the Electronic Charge Density.
Journal of Computational Chemistry, 2012Co-Authors: David Vega, Yosslen Aray, Jesús RodríguezAbstract:The topological study of the Electronic Charge Density is useful to obtain information about the kinds of bonds (ionic or covalent) and the atom Charges on a molecule or crystal. For this study, it is necessary to calculate, at every space point, the Electronic Density and its Electronic Density derivatives values up to second order. In this work, a grid-based method for these calculations is described. The library, implemented for three dimensions, is based on a multidimensional Lagrange interpolation in a regular grid; by differentiating the resulting polynomial, the gradient vector, the Hessian matrix and the Laplacian formulas were obtained for every space point. More complex functions such as the Newton–Raphson method (to find the critical points, where the gradient is null) and the Cash–Karp Runge–Kutta method (used to make the gradient paths) were programmed. As in some crystals, the unit cell has angles different from 90°, the described library includes linear transformations to correct the gradient and Hessian when the grid is distorted (inclined). Functions were also developed to handle grid containing files (grd from DMol® program, CUBE from Gaussian® program and CHGCAR from VASP® program). Each one of these files contains the data for a molecular or crystal Electronic property (such as Charge Density, spin Density, electrostatic potential, and others) in a three-dimensional (3D) grid. The library can be adapted to make the topological study in any regular 3D grid by modifying the code of these functions. © 2012 Wiley Periodicals, Inc.
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Adsorption of Thiophene on the RuS2 (100) and (111) Surfaces: A Laplacian of the Electronic Charge Density Study
The Journal of Physical Chemistry B, 2002Co-Authors: Yosslen Aray, Jesús Rodríguez, David Vega, Santiago Coll, ‖ And Eloy Nouel Rodríguez-arias, Felix RosilloAbstract:To study the effect of the surface Ru sulfur coordination number and of the surface S−H and Ru−H species into the thiophene adsorption on RuS2, a topologic study of the Laplacian of the Electronic Density of selected (100) and (111) surfaces was carried out. It was found that a nonbonded local Charge concentration on the S atom of the thiophene interacts with a local minimum on the outermost Ru atoms of the surfaces. This interaction is strongly affected by a nonbonded local Charge concentration located on the outermost S atoms of the surface. Both interactions combine in such way that the strength of the thiophene adsorption on the unhydrogenated surfaces shows small changes. The main role of the S−H bond is to move away the surface sulfur local Charge concentrations from the Ru atoms while the Ru−H species favors the hydride attacks to a local minimum located at the Cα of the thiophene molecule.
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Study of Hydrodesulfurization by Transition Metal Sulfides by Means of the Laplacian of the Electronic Charge Density
ChemPhysChem, 2001Co-Authors: Yosslen Aray, Jesús RodríguezAbstract:The typical volcano plot for the catalytic hydrodesulfurization activity of transition metal sulfides (TMSs) results from different nature of the TM-S interactions in layered and isotropic TMSs. This was the conclusion of a topological analysis of the Laplacian of the Electronic Charge Density of 4d TMSs. For layered TMSs (for example MoS2), the S atom of thiophene interacts with a local Charge concentration on the TM (as shown in the picture) whereas in the case of isotropic TMSs, such as RuS2, it interacts with a local Charge minimum.
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Laplacian of the Electronic Charge Density and Heat of Adsorption of O2 and CO Molecules on 3d Transition Metals
The Journal of Physical Chemistry B, 2000Co-Authors: Yosslen Aray, And Jesus Rodriguez, David VegaAbstract:A topological analysis of the Laplacian of the Electronic Charge Density of bulk 3d transition metals has been performed. This analysis shows that the atomic graph for the atoms of the fcc metals (Ni and Cu) is an octahedron with six vertexes (corresponding to local Charge concentrations) linked by twelve edges and bounded by eight faces (corresponding to local Charge minima). For the bcc case (V, Cr, and Fe), the corresponding graph is a cube with eight vertexes, twelve edges, and six faces. For the early hcp metals (Sc and Ti), the graph is a trigonal bipyramid with five vertexes, nine edges, and six faces, whereas for Co, it is a trigonal prism with six vertexes, nine edges, and five faces. Despite the different kinds of the graphs obtained, we have been able to correlate the value of the Laplacian at the local minima with the experimental heats of adsorption (which show a systematic decrease) for the O2 and CO molecules on the 3d transition metals. This result suggests that the bonds formed by these m...
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Study of CO adsorption on the Fe(100) surface using the Laplacian of the Electronic Charge Density
Surface Science, 1998Co-Authors: Yosslen Aray, Jesús RodríguezAbstract:The interaction of a CO molecule with the Fe(100) surface is analyzed by the topology of the Laplacian of the Electronic Charge Density −∇2ρ. This analysis shows that the atomic graph of the top atoms of the Fe(100) surface is a cube that exposes a face, Ftop, with a “hole” of Charge or (3,+1) critical point of −∇2ρ, whereas the corresponding graph for the second layer atoms is an octahedron that exhibits a vertex, Vsec, protruding above the Fe(100) surface, with a “peak” of Charge or (3,−3) critical point of −∇2ρ. Atomic graphs determined for the CO molecule show that the carbon atom has a non-bonded vertex, CVnb, and a torus, Ctorus, of Charge depletion perpendicular to the C–O bond direction. As the CO molecule approaches the surface, electron transfer towards the tilted CO in turn induces two non-bonded critical points, OVnb, on the O atom. In accordance with experimental and theoretical results, the topological theory of the Laplacian suggests that the preferred pathway for CO dissociation corresponds to the tilted orientation on the surface, in which the attractive interaction Ctorus–Vsec is enhanced by the interaction of the two OVnb with the Ftop on two Fe top atoms of the (100) surface.
Jesús Rodríguez - One of the best experts on this subject based on the ideXlab platform.
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C library for topological study of the Electronic Charge Density.
Journal of Computational Chemistry, 2012Co-Authors: David Vega, Yosslen Aray, Jesús RodríguezAbstract:The topological study of the Electronic Charge Density is useful to obtain information about the kinds of bonds (ionic or covalent) and the atom Charges on a molecule or crystal. For this study, it is necessary to calculate, at every space point, the Electronic Density and its Electronic Density derivatives values up to second order. In this work, a grid-based method for these calculations is described. The library, implemented for three dimensions, is based on a multidimensional Lagrange interpolation in a regular grid; by differentiating the resulting polynomial, the gradient vector, the Hessian matrix and the Laplacian formulas were obtained for every space point. More complex functions such as the Newton–Raphson method (to find the critical points, where the gradient is null) and the Cash–Karp Runge–Kutta method (used to make the gradient paths) were programmed. As in some crystals, the unit cell has angles different from 90°, the described library includes linear transformations to correct the gradient and Hessian when the grid is distorted (inclined). Functions were also developed to handle grid containing files (grd from DMol® program, CUBE from Gaussian® program and CHGCAR from VASP® program). Each one of these files contains the data for a molecular or crystal Electronic property (such as Charge Density, spin Density, electrostatic potential, and others) in a three-dimensional (3D) grid. The library can be adapted to make the topological study in any regular 3D grid by modifying the code of these functions. © 2012 Wiley Periodicals, Inc.
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Adsorption of Thiophene on the RuS2 (100) and (111) Surfaces: A Laplacian of the Electronic Charge Density Study
The Journal of Physical Chemistry B, 2002Co-Authors: Yosslen Aray, Jesús Rodríguez, David Vega, Santiago Coll, ‖ And Eloy Nouel Rodríguez-arias, Felix RosilloAbstract:To study the effect of the surface Ru sulfur coordination number and of the surface S−H and Ru−H species into the thiophene adsorption on RuS2, a topologic study of the Laplacian of the Electronic Density of selected (100) and (111) surfaces was carried out. It was found that a nonbonded local Charge concentration on the S atom of the thiophene interacts with a local minimum on the outermost Ru atoms of the surfaces. This interaction is strongly affected by a nonbonded local Charge concentration located on the outermost S atoms of the surface. Both interactions combine in such way that the strength of the thiophene adsorption on the unhydrogenated surfaces shows small changes. The main role of the S−H bond is to move away the surface sulfur local Charge concentrations from the Ru atoms while the Ru−H species favors the hydride attacks to a local minimum located at the Cα of the thiophene molecule.
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Study of Hydrodesulfurization by Transition Metal Sulfides by Means of the Laplacian of the Electronic Charge Density
ChemPhysChem, 2001Co-Authors: Yosslen Aray, Jesús RodríguezAbstract:The typical volcano plot for the catalytic hydrodesulfurization activity of transition metal sulfides (TMSs) results from different nature of the TM-S interactions in layered and isotropic TMSs. This was the conclusion of a topological analysis of the Laplacian of the Electronic Charge Density of 4d TMSs. For layered TMSs (for example MoS2), the S atom of thiophene interacts with a local Charge concentration on the TM (as shown in the picture) whereas in the case of isotropic TMSs, such as RuS2, it interacts with a local Charge minimum.
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Study of CO adsorption on the Fe(100) surface using the Laplacian of the Electronic Charge Density
Surface Science, 1998Co-Authors: Yosslen Aray, Jesús RodríguezAbstract:The interaction of a CO molecule with the Fe(100) surface is analyzed by the topology of the Laplacian of the Electronic Charge Density −∇2ρ. This analysis shows that the atomic graph of the top atoms of the Fe(100) surface is a cube that exposes a face, Ftop, with a “hole” of Charge or (3,+1) critical point of −∇2ρ, whereas the corresponding graph for the second layer atoms is an octahedron that exhibits a vertex, Vsec, protruding above the Fe(100) surface, with a “peak” of Charge or (3,−3) critical point of −∇2ρ. Atomic graphs determined for the CO molecule show that the carbon atom has a non-bonded vertex, CVnb, and a torus, Ctorus, of Charge depletion perpendicular to the C–O bond direction. As the CO molecule approaches the surface, electron transfer towards the tilted CO in turn induces two non-bonded critical points, OVnb, on the O atom. In accordance with experimental and theoretical results, the topological theory of the Laplacian suggests that the preferred pathway for CO dissociation corresponds to the tilted orientation on the surface, in which the attractive interaction Ctorus–Vsec is enhanced by the interaction of the two OVnb with the Ftop on two Fe top atoms of the (100) surface.
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numerical determination of the topological properties of the Electronic Charge Density in molecules and solids using Density functional theory
Journal of Physical Chemistry A, 1997Co-Authors: Yosslen Aray, Jesús Rodríguez, Juan RiveroAbstract:A numerical method to analyze the topology of the Electronic Density regardless of how it was obtained (analytically or numerically) was implemented for the Extreme 94 program. The method allows th...