Investigation of intermolecular interactions based on the atomic statistical model

Possibilities of improving individual contributions to the statistical interaction energy (kinetic and exchange) are examined. A new method of calculating statistical interaction energies is proposed. The exchange term is calculated using a suitably modified second-order gradient correction. For the kinetic contribution the accurate formula corresponding to the first-order perturbation theory is applied. The calculations have been carried out for several pairs of noble gas atoms.     

Oxygen Atom Exchange Mechanism in Reaction of OH Radical with AsO

IntroductionNitrous acid,HONO,has been extensivelystudied by means of experimental[1,2 ] andtheoretical methods due to its importance inatomspheric chemistry[3 ] . Those studies includedits experimental spectroscopy[1,2 ] and potentialenergy surface with the aid of density functionaltheory[3 ] . Its phosphorus analogue,HOPO,hasbeen studied by virtue of theoreticalcomputations[4] ,and detected in the gas by infraredlaser spectroscopy in2 0 0 0 by Bell and coworkers[5]and matrix isolation in…     

The importance of fully quantitative non-local treatments of exchange energy in Density Functional Theory of atoms,molecules and clusters,characterised by strongly inhomogeneous electron liquids

After a brief summary of some recent work on non-local approximations to the exchange energy and potential in density functional theory, a table is presented for atoms from Be to Ar, with an even number of electrons, having large electron density gradients, which highlights the importance of exchange. Until non-local exchange energy is truly quantitative, refinements of correlation energy may be submerged through ‘noisy’ exchange.     

Regional self-interaction correction of density functional theory

We propose a new simple scheme for self-interaction correction (SIC) of exchange functionals in the density functional theory. In the new scheme, exchange energies are corrected by substituting exchange self-interactions for exchange functionals in regions of self-interaction. To classify the regions of self-interaction, we take advantage of the property of the total kinetic energy density approaching the Weizs?cker density in the case of electrons in isolated orbitals. The scheme differs from conventional SIC methods in that it produces optimized molecular structures. Applying the scheme to the calculation of reaction energy barriers showed that it provides a clear improvement in cases where the barriers are underestimated by conventional "pure" functionals. In particular, we found that this scheme even reproduces a transition state that is not given by pure functionals.     

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.     

密度泛函理论预测微量元素在Al(100)表面的偏聚

通过周期性层状模型, 利用密度泛函理论预测了微量杂质元素原子M(M=Fe, Si, Mg, Cu, Mn, Ga, In, Sn, Pb)在高纯铝箔(100)表面的偏聚趋势. 计算得到表面偏聚能与已有实验结果相吻合. 表面偏聚能由表面取代的微量元素原子M的位置、原子半径和金属的表面能决定. 当表面偏聚能为负时, 微量元素原子M在表面偏聚, 反之则杂质原子不发生表面聚集. 微量元素原子在铝箔表面偏聚可以使铝箔表面产生大量的缺陷和位错, 它们在铝箔腐蚀时容易成为腐蚀的形核起点, 进而增加铝箔的腐蚀发孔密度.     

Extended Fe₄ butterfly complexes: theoretical analysis of magnetic properties and magnetostructural maps

The inclusion of additional metal atoms in Fe? butterfly complexes drastically modifies their magnetic properties. Exchange interactions of a Fe?Y? complex have been calculated using theoretical methods based on density functional theory. The calculated values are in good agreement with experimental data showing that the change in the nature of bridging ligands induces a dramatic decrease of the antiferromagnetic wing-body interaction while the body-body interaction between the two central iron atoms is ferromagnetic. Finally, we propose a new tool to facilitate the understanding of the magnetic properties in polynuclear iron complexes. Magnetostructural maps allow us to correlate the calculated exchange coupling constants with metal-metal distances for the dinuclear or polynuclear iron complexes that we have studied.     

An ab initio potential surface describing abstraction and exchange for H+CH4

We report an ab initio-based global potential energy surface for H+CH4 that describes the abstraction and exchange reactions. The PES, which is invariant with respect to any permutation of five H atoms, is a fit to 20,728 electronic energies calculated using the partially spin-restricted coupled-cluster method (RCCSD(T)) with a moderately large basis (aug-cc-pVTZ). A first set of quasiclassical trajectory calculations using this PES are reported for the H+CD4-->HD+CD3 reaction at collision energies of 0.65 and 1.52 eV and are compared to experiment and recent direct dynamics calculations done with density functional theory.     

DFT calculation of the electronic and optical properties of Ag2PdO2 from X-ray and neutron crystallographic data

Electronic and optical properties of ternary silver palladium oxide (Ag₂PdO₂) are investigated using density functional theory. Two different possible approximations for the exchange correlation potentials were employed. The X-ray and neutron crystallographic data were optimized by minimization of the forces (1 mRy/a.u.) acting on the atoms. The electronic structure, electron space charge density, chemical bonding and optical dielectric were determined from the relaxed geometry seeking deep insight understanding of this material. Our calculated energy band gap (0.15 eV) shows a good agreement with the experimental value (0.18 eV).     

Orbital-dependent correlation energy in density-functional theory based on a second-order perturbation approach: success and failure

We have developed a second-order perturbation theory (PT) energy functional within density-functional theory (DFT). Based on PT with the Kohn-Sham (KS) determinant as a reference, this new ab initio exchange-correlation functional includes an exact exchange (EXX) energy in the first order and a correlation energy including all single and double excitations from the KS reference in the second order. The explicit dependence of the exchange and correlation energy on the KS orbitals in the functional fits well into our direct minimization approach for the optimized effective potential, which is a very efficient method to perform fully self-consistent calculations for any orbital-dependent functionals. To investigate the quality of the correlation functional, we have applied the method to selected atoms and molecules. For two-electron atoms and small molecules described with small basis sets, this new method provides excellent results, improving both second-order Moller-Plesset expression and any conventional DFT results significantly. For larger systems, however, it performs poorly, converging to very low unphysical total energies. The failure of PT based energy functionals is analyzed, and its origin is traced back to near degeneracy problems due to the orbital- and eigenvalue-dependent algebraic structure of the correlation functional. The failure emerges in the self-consistent approach but not in perturbative post-EXX calculations, emphasizing the crucial importance of self-consistency in testing new orbital-dependent energy functionals.     

Theoretical studies on the magnetic bistability of dinickel complex tuned by azide

The magnetic-structural correlation in magnetic switchable dinickel(II) complex [LNi2(N3)3] (L- is a pyrazolate-based compartmental ligand) has been investigated on the basis of various unrestricted density functional theory (UDFT) combined with the broken symmetry (BS) approach. The calculated exchange coupling constants were in good agreement with experimental result by using the PBE0 method with LANL2DZ basis set. The antiferromagnetic interaction between the Ni(II) ions is mainly due to the large energy difference of the singly occupied molecular orbitals (SOMOs), and the p orbital overlap for nitrogen atoms on azido and the pyrazolate bridge groups. The analysis of the spin density distribution reveals that both the spin polarization and spin delocalization contribute to the antiferromagnetic interaction. Furthermore, the bistable magnetic behavior for this system (strong antiferromagnetic interaction in low-temperature phase and the week antiferromagnetic in high-temperature phase) results from the change of the Ni-NNN-Ni dihedral angle (tau) in mu1,3-N3. The increase of tau is the key role in decreasing the SOMOs energy difference and weakening the antiferromagnetic interaction. Therefore, the abrupt modulation of the magnitude of M-NNN-M dihedral angle tau in the binuclear-azide complex by external perturbations provides new possibilities for the design of molecular magnetic switching devices.     

Spin-orbit relativistic long-range corrected time-dependent density functional theory for investigating spin-forbidden transitions in photochemical reactions

A long-range corrected (LC) time-dependent density functional theory (TDDFT) incorporating relativistic effects with spin-orbit couplings is presented. The relativistic effects are based on the two-component zeroth-order regular approximation Hamiltonian. Before calculating the electronic excitations, we calculated the ionization potentials (IPs) of alkaline metal, alkaline-earth metal, group 12 transition metal, and rare gas atoms as the minus orbital (spinor) energies on the basis of Koopmans' theorem. We found that both long-range exchange and spin-orbit coupling effects are required to obtain Koopmans' IPs, i.e., the orbital (spinor) energies, quantitatively in DFT calculations even for first-row transition metals and systems containing large short-range exchange effects. We then calculated the valence excitations of group 12 transition metal atoms and the Rydberg excitations of rare gas atoms using spin-orbit relativistic LC-TDDFT. We found that the long-range exchange and spin-orbit coupling effects significantly contribute to the electronic spectra of even light atoms if the atoms have low-lying excitations between orbital spinors of quite different electron distributions.     

A DFT variational approach to Hooke''s atom based on local-scaling transformations

The local-scaling transformation version of density functional theory, LS-DFT, is employed in order to construct energy functionals for Hooke's atom. The components of the energy are analyzed and the resulting exchange and correlation potentials are compared with the exact ones. In addition, the representation of the exact one-particle density in terms of the various components of the total energy density is discussed.     

Charging energy and barrier height of pentacene on Au(111): a local-orbital hybrid-functional density functional theory approach

We analyze the pentacene/Au(111) interface by means of density functional theory (DFT) calculations using a new hybrid functional; in our approach we introduce, in a local-orbital formulation of DFT, a hybrid exchange potential, and combine it with a calculation of the molecule charging energy to properly describe the transport energy gap of pentacene on Au(111). Van der Waals forces are taken into account to obtain the adsorption geometry. Interface dipole potentials are also calculated; it is shown that the metal/pentacene energy level alignment is determined by the potential induced by the charge transfer between the metal surface and the organic material, as described by the induced density of interface states model. Our results compare well with the experimental data.     

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.     

Improved local density functional approach for atomic systems

Through a new local density approximation to the kinetic energy density functional introduced by us recently, a simple Thomas–Fermi-like scheme for the direct calculation of electron density in atoms is proposed. The calculated density is nonsingular at the nucleus and the energy values are in very good agreement with the corresponding Hartree–Fock results for atoms. © 1994 John Wiley & Sons, Inc.     

Strength and nature of hydrogen bonding interactions in mono- and di-hydrated formamide complexes

In this work, mono- and di-hydrated complexes of the formamide were studied. The calculations were performed at the MP2/6-311++G(d,p) level of approximation. The atoms in molecules theory (AIM), based on the topological properties of the electronic density distribution, was used to characterize the different types of bonds. The analysis of the hydrogen bonds (H-bonds) in the most stable mono- and di-hydrated formamide complexes shows a mutual reinforcement of the interactions, and some of these complexes can be considered as "bifunctional hydrogen bonding hydration complexes". In addition, we analyzed how the strength and the nature of the interactions, in mono-hydrated complexes, are modified by the presence of a second water molecule in di-hydrated formamide complexes. Structural changes, cooperativity, and electron density redistributions demonstrate that the H-bonds are stronger in the di-hydrated complexes than in the corresponding mono-hydrated complexes, wherein the σ- and π-electron delocalization were found. To explain the nature of such interactions, we carried out the atoms in molecules theory in conjunction with reduced variational space self-consistent field (RVS) decomposition analysis. On the basis of the local Virial theorem, the characteristics of the local electron energy density components at the bond critical points (BCPs) (the 1/4? (2)ρ(b) component of electron energy density and the kinetic energy density) were analyzed. These parameters were used in conjunction with the electron density and the Laplacian of the electron density to analyze the characteristics of the interactions. The analysis of the interaction energy components for the systems considered indicates that the strengthening of the hydrogen bonds is manifested by an increased contribution of the electrostatic energy component represented by the kinetic energy density at the BCP.