A semiclassical density functional evaluation of the smoothly varying part of the Hartree–Fock binding energy in atoms

A semiclassical density functional approach is used to evaluate the smooth part of the variation of the Hartree–Fock (HF ) binding energy in atoms, from helium through xenon. The energy density functional is chosen with an improved form for the kinetic energy functional (KEF ). The variation of the HF binding energy is split into smooth and oscillating (shell-structure) parts, in accordance with Strutinskyøs self-consistent averaging procedure, which is equivalent to a semiclassical ?-expansion of the KEF . This enables a well-grounded evaluation of the oscillating part of the HF binding energy, which displays a quasi-periodic behavior expressing clearly the shell structure of atoms. © 1994 John Wiley & Sons, Inc.     

A First‐Principles Study of Lithium Adsorption on a Graphene–Fullerene Nanohybrid System

The mechanism of Li adsorption on a graphene–fullerene (graphene–C₆₀) hybrid system has been investigated using density functional theory (DFT). The adsorption energy for Li atoms on the graphene–C₆₀ hybrid system (?2.285 eV) is found to be higher than that on bare graphene (?1.375 eV), indicating that the Li adsorption on the former system is more stable than on the latter. This is attributed to the high affinity of Li atoms to C₆₀ and the charge redistribution that occurs after graphene is mixed with C₆₀. The electronic properties of the graphene–C₆₀ system such as band structure, density of states, and charge distribution have been characterized as a function of the number of Li atoms adsorbed in comparison to those of the pure graphene and C₆₀. Li adsorption is found to preferentially occur on the C₆₀ side due to the high adsorption energy of Li on C₆₀, which imparts a metallic character to the C₆₀ in the graphene–C₆₀ hybrid system.     

Note on the Fermi–Amaldi correction for the Thomas–Fermi theory of atoms

The aim of this note is to ascertain the importance of the Fermi–Amaldi (FA ) correction for the Thomas–Fermi (TF ) theory of atoms. For this purpose, an analytic trial electron density has been chosen and the Thomas–Fermi–Amaldi (TFA ) energy expression has been minimized by the Ritz method for the closed-shell atoms Ne, Ar, Kr, Xe, and Rn. The variationally obtained electron densities have then been used for calculating the diamagnetic susceptibilities of these atoms. The calculated values show only a very small improvement over values calculated by Jensen by an analogous procedure from the TF energy expression.     

A DFT study of adsorption and decomposition of nitroamine molecule on Mg(001) surface

The adsorption and dissociation mechanism of NH₂NO₂ on the Mg surface have been investigated by the generalized gradient approximation of density functional theory. Calculations employ a supercell (3 × 3 × 3) slab model and three-dimensional periodic boundary conditions. The strong attractive force between oxygen and Mg atoms induces the N–O bond of the NH₂NO₂ to decompose. The dissociated oxygen atoms and radical fragment of NH₂NO₂ oxidize readily Mg atoms. The largest adsorption energy is ?860.5 kJ/mol. The largest charge transfer is 3.76 e from surface Mg atoms to fragments of NH₂NO₂. The energy barriers of N–O bond dissociation are in a range of 11.6–36.5 kJ/mol. The adsorption energy of NH₂NO₂ on the Mg surface compensates the energy needed for the N–O bond dissociation.     

Four-dimensional density and energy density functional

The relations based on an external one-electron operator V( r ) are examined from two view-points, i.e., from the Hohenberg–Kohn approach and the four-dimensional density concept introduced by Wilson and Frost, and extensively studied by Parr and Politzer. The object being to obtain, with the help of the Hellmann–Feynman theorem, new formulas for the energy of atoms and molecules, and to discuss the construction of the universal energy density functional on the basis of the four-dimensional density.     

Density functional theory for molecular and periodic systems using density fitting and continuous fast multipole method: Analytical gradients

A full implementation of analytical energy gradients for molecular and periodic systems is reported in the TURBOMOLE program package within the framework of Kohn–Sham density functional theory using Gaussian‐type orbitals as basis functions. Its key component is a combination of density fitting (DF) approximation and continuous fast multipole method (CFMM) that allows for an efficient calculation of the Coulomb energy gradient. For exchange‐correlation part the hierarchical numerical integration scheme (Burow and Sierka, Journal of Chemical Theory and Computation 2011, 7, 3097) is extended to energy gradients. Computational efficiency and asymptotic O(N) scaling behavior of the implementation is demonstrated for various molecular and periodic model systems, with the largest unit cell of hematite containing 640 atoms and 19,072 basis functions. The overall computational effort of energy gradient is comparable to that of the Kohn–Sham matrix formation. © 2016 Wiley Periodicals, Inc.     

Atomic calculations with an effective one-body potential

The accuracy of a new effective one-body potential is assessed by the study of the electronic structure of atoms from He to Kr. The exchange part of this potential is obtained from a local approximation. Several simplified representations of the electronic density which lead to analytic Coulomb potentials are tested. It is shown that the introduction of the shell structure of the density is necessary, at least for third row atoms. The screening parameters of the potential are variationally optimized with respect to the total energy of the atom. With the most elaborate form of the Coulomb potential which contains one screening parameter for each shell, the comparison of the results with exact Hartree–Fock calculations is very promising. The relative difference is on the order of 10^?5 for the total energy and on the order of 10^?2 for the orbital energies. Multiplet splitting is reproduced accurately and F^? is predicted to be stable (in contrast some others local potentials) by an amount of 0.046 a.u., compared with 0.050 a.u. for an exact Hartree–Fock calculation.     

Microstructure and surface roughness of graphite‐like carbon films deposited on silicon substrate by molecular dynamic simulation

Molecular dynamics simulations are performed on the atomic origin of the growth process of graphite‐like carbon film on silicon substrate. The microstructure, mass density, and internal stress of as‐deposited films are investigated systematically. A strong energy dependence of microstructure and stress is revealed by varying the impact energy of the incident atoms (in the range 1–120 eV). As the impact energy is increased, the film internal stress converts from tensile stress to compressive stress, which is in agreement with the experimental results, and the bonding of C‐Si in the film is also increased for more substrate atoms are sputtered into the grown film. At the incident energy 40 eV, a densification of the deposited material is observed and the properties such as density, sp³ fraction, and compressive stress all reach their maximums. In addition, the effect of impact energy on the surface roughness is also studied. The surface morphology of the film exhibits different characteristics with different incident energy. When the energy is low (<40 eV), the surface roughness is reduced with the increasing of incident energy, and it reaches the minimum at 50 eV. Copyright © 2012 John Wiley & Sons, Ltd.     

Quadrupole and octupole Cauchy moments of the atoms through argon

Quadrupole and octupole Cauchy moments of the atoms through argon are calculated using the hydrodynamic formulation of time-dependent Kohn–Sham theory. The exchange-correlation energy density functional is approximated by a gradient expansion for atoms that has an explicit dependence upon the number of electrons. The first-order corrections to the Kohn–Sham amplitudes and phases are found by seeking variational solutions of the derived sequential set of functionals. The trial functions employed contain both linear and nonlinear variational parameters and are thus flexible enough to provide rapid convergence to the multipole polarizabilities. The resulting Cauchy moments provide information that allows the calculation of various properties that result from the linear interaction of atoms with a time-varying electric field. © 1994 John Wiley & Sons, Inc.     

Noncovalent Bonds between Tetrel Atoms

The pairing of TFH₃ with a TH₂CH₃⁻ anion, where T represents tetrel atoms C, Si, Ge, Sn, Pb, results in a strong direct interaction between the two T atoms. The interaction energy is sensitive to the nature of the two T atoms but can be as large as 90 kcal/mol. The noncovalent bond strength rises quickly as the basic T atom of the anion becomes smaller, or as the Lewis acid T grows larger, although there is less sensitivity to the latter atom. The electrostatic component makes up some 55–70 % of the total attraction energy. This term is well accounted for by simple combination of the maximum and minimum values of the molecular electrostatic potential of the Lewis acid and base units, respectively. The complexation induces a rearrangement in the TFH₃ molecule from tetrahedral to trigonal pyramidal. The associated deformation energy reduces the exothermicity of the complexation reaction. Electron density shift patterns reveal a density loss on the basic T atom, along with accompanying increases on the acidic T and its attached F atom.     

Energy Stabilities,Magnetic Properties,and Electronic Structures of Diluted Magnetic Semiconductor Zn1-xMnxS(001) Thin Films

We investigate the electronic and magnetic properties of the diluted magnetic semiconductors Zn_1-xMn_xS(001) thin films with different Mn doping concentrations using the total energy density functional theory. The energy stability and density of states of a single Mn atom and two Mn atoms at various doped configurations and different magnetic coupling state were calculated. Different doping configurations have different degrees of p-d hybridization, and because Mn atoms are located in different crystal-field environment, the 3d projected densities of states peak splitting of different Mn doping configurations are quite different. In the two Mn atoms doped, the calculated ground states of three kinds of stable configurations are anti-ferromagnetic state. We analyzed the 3d density of states diagram of three kinds of energy stability configurations with the two Mn atoms in different magnetic coupling state. When the two Mn atoms are ferromagnetic coupling, due to d-d electron interactions, density of states of anti-bonding state have significant broadening peaks. As the concentration of Mn atoms increases, there is a tendency for Mn atoms to form nearest neighbors and cluster around S. For such these configurations, the antiferromagnetic coupling between Mn atoms is energetically more favorable.     

Geometric stability of PtFe/PdFe embedded in graphene and catalytic activity for CO oxidation

The direct methanol fuel cell (DMFC) is considered as a promising power source, because of its abundant fuel source, high energy density and environmental friendliness. Among DMFC anode materials, Pt and Pt group metals are considered to be the best electrocatalysts. The combination of Pt with some specific transition metal can reduce the cost and improve the tolerance toward CO poisoning of pure Pt catalysts. In this paper, the geometric stabilities of PtFe/PdFe atoms anchored in graphene sheet and catalytic CO oxidation properties were investigated using the density functional theory method. The results show that the Pt (Pd) and Fe atoms can replace C atoms in graphene sheet. The CO oxidation reaction by molecular O₂ on PtFe–graphene and PdFe–graphene was studied. The results show that the Eley–Rideal (ER) mechanism is expected over the Langmuir–Hinshelwood mechanism for CO oxidation on both PtFe–graphene and PdFe–graphene. Further, complete CO oxidation on PtFe–graphene and PdFe–graphene proceeds via a two‐step ER reaction: CO(gas) + O₂(ads) → CO₂(ads) + O(ads) and CO(gas) + O(ads) → CO₂(ads). Our results reveal that PtFe/PdFe commonly embedded in graphene can be used as a catalyst for CO oxidation. The microscopic mechanism of the CO oxidation reaction on the atomic catalysts was explored.     

Theoretically Calculated Deformation Density of Small Molecules

Analysis of the theoretical electron deformation density based on EHMO and ab initio calculations has been applied to the simple molecules F₂, H₂O and SO₂ The effects from varied basis sets for such deformation density were sought. The accumulation of electron density between the bonded atoms calculated from EHMO and ab initio methods with STO-3G is generally under-estimated. Such phenomena are significantly improved by using split-valence basis sets e.g. 3–21G and 4–31G. The addition of d polarization functions is apparently important for the sulfur atom in sulfur-related bonding. 3–21G or 3–21G^* basis sets were found to provide not only valuable deformation density distributions of molecules but also comparable orbital energy states with respect to the experimental values.     

O2 dissociative adsorption on the Cu‐, Ag‐, and W‐doped Al(111) surfaces from DFT computation

The O₂ adsorption and dissociation on M‐doped (M = Cu, Ag, W) Al(111) surface were studied by density functional theory. The adsorption energy of adsorbate, the average binding energy and surface energy of Al surface, and the doping energy of doping atom were calculated. All the doped atoms can be stably combined with Al atoms, while being slightly embedded in the surface to a certain depth. The TOP‐type surfaces are the most stable doped surfaces for O₂ adsorption, which is related to the orbital hybridization between the adsorbate and the surface atoms, the electronegativity, and the orbital energy level of the doping atoms. Moreover, the O atoms and doping atoms contribute significantly to the density of states (DOS), especially the O‐p orbital electrons and the d orbital electrons of doping atoms. The degree of O₂ dissociation is related to the doping atoms on Al surfaces, and the doping atoms actually resist the dissociation of O₂. W atoms have the best resistance effect on the O₂ dissociation as compared with Cu and Ag atoms, especially W‐1NN surface, which has both large barrier energy and reaction energy.     

Superhalogen properties of PdFn (n=1–7) clusters using Quantum chemical method

In this work the interaction of Palladium (Pd) atom with Fluorine (F) has been studied using density functional theory. Up to seven F atoms are bound to a single Pd atom which results in increase of electron affinities of given molecule successively, reaching a peak value of 8.54 eV for PdF₇. By using HOMO–LUMO gap, molecular orbital analysis, binding energy of these clusters, we examined its stability and reactivity. It is found that energy required for dissociation of F₂ molecules are higher than energy required for dissociation of F atoms. The unusual properties brought about by involvement of inner shell 4d-electrons, which not only allow PdF_n clusters to belong to the class of superhalogens but also show that its valence can exceed the nominal value of 1.     

Coulomb-Hole–Hartree–Fock functional

We have extended to molecules a density functional previously parametrized for atomic computations. The Coulomb-hole–Hartree–Fock functional, introduced by Clementi in 1963, estimates the dynamical correlation energy by the computations of a Hartree–Fock-type single-determinant wave function, where the Hartree–Fock potential was augmented with an effective potential term, related to a hard Coulomb hole enclosing each electron. The method was later revisited by S. Chakravorty and E. Clementi [Phys. Rev. A 39 , 2290 (1989)], where a Yukawa-type soft Coulomb hole replaced the previous hard hole; atomic correlation energies, computed for atoms with Z = 2 to Z = 54 as well as for a number of excited states, validated the method. In this article, we parametrized a function, which controls the width of the soft Coulomb hole, by fitting the first and second atomic ionization potentials of the atoms with 1 ? Z ? 18. The parametrization has been preliminarily validated by computing the dissociation energy for a number of molecules. A few-determinant version of the Coulomb-hole–Hartree–Fock method, necessary to account for the nondynamic correlation corrections, is briefly discussed. © 1994 John Wiley & Sons, Inc.     

Hartree–Fock wave functions with a modified GTO basis for atoms

We have solved the atomic Hartree–Fock equations by using the algebraic approach, expanding the single-particle radial wave function in terms of a modified Gaussian type orbitals (GTOs) basis. Several atomic properties such as Kato's cusp condition for the electron density or the correct asymptotic behavior of the electron momentum density distribution are accurately verified. Additionally the energy of the atomic ground state can be obtained by using a smaller number of basis functions than in standard GTO expansions. This study has been performed for several atoms of the first three rows. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 59–64, 1997     

Proton transfer in small model systems: A density functional study

The structures, interaction energies, and proton-transfer features of some representative intermolecular complexes are determined by using a density functional which incorporates gradient corrections and, as recently suggested by Becke, some Hartree–Fock exchange. The results are compared with those obtained by high-order many-body perturbation theory and by a number of more conventional density functionals. Hydrogen-bond strengths and interatomic distances between heavy atoms are well reproduced by several density functionals. However, inclusion of some Hartree–Fock exchange is mandatory to improve XH bond lengths, and, especially, energy barriers governing proton transfer. Use of the new functional significantly improves the agreement with experimental and post-Hartree–Fock results. This paves the route for a detailed theoretical study of proton-transfer processes in large, biologically significant systems. © 1995 John Wiley & Sons, Inc.     

Study of the kinetic energy densities of electrons as applied to quantum dots in a magnetic field

There are three expressions for the kinetic energy density t( r ) expressed in terms of its quantal source, the single-particle density matrix: t _A( r ) , the integrand of the kinetic energy expectation value; t _B( r ) , the trace of the kinetic energy tensor; t _C( r ) , a virial form in terms of the ‘classical’ kinetic field. These kinetic energy densities are studied by application to ‘artificial atoms‘ or quantum dots in a magnetic field in a ground and excited singlet state. A comparison with the densities for natural atoms and molecules in their ground state is made. The near nucleus structure of these densities for natural atoms is explained. We suggest that in theoretical frameworks which employ the kinetic energy density such as molecular fragmentation, density functional theory, and information-entropic theories, one use all three expressions on application to quantum dots, and the virial expression for natural atoms and molecules. New physics could thereby be gleaned.