Unrestricted Hartree-Fock approximation of the extended emery model

We use an unrestricted self-consistent Hartree-Fock approach to calculate the nature of doping states in the three-band Hubbard model. It turns out that for physically relevant parameter values one hole is localized within a small spin-polarized region where five Cu spins are aligned in the same direction. The spin polarization and binding energy between these spinpolaronic states are investigated as a function of different parameters including a Holstein-type electron-phonon coupling on the Cu sites. At higher doping concentration we observe the occurrence of afmon states where the holes are localized in a ring-shaped area. Inside this ring the antiferromagnetic order parameter has inverse sign with respect to the residual antifer-romagnetically ordered plane.     

1-乙基-3-甲基咪唑和PF-6离子液体的理论研究

采用Hartree-Fock和密度泛函理论方法研究1-乙基-3-甲基咪唑阳离子(EMIM )、PF6-、EMIM -PF6-离子对。氢原子、碳原子、氮原子、氟原子和磷原子在6-31 (d,p)基组水平上,采用Gaussian94软件包给EMIM 、PF6-及12个EMIM -PF6-离子的初始结构做全优化和频率分析。比较研究所优化结构和能量的性质。计算结果表明最低能量结构的EMIM -PF6-阴阳离子对相互作用能,在Hartree-Fock水平上为326.6 kJ／mol、在密度泛函理论上为328.8 kJ／mol。阳离子不对称、阴阳离子间距较大、阴阳离子电荷的分散使①静电作用降低,导致离子液体熔点较低。②EMIM 氢原子的正电荷增加、PF6-氟原子的负电荷增加,导致C-H---F氢键相互作用增强。从而在离子液体中起重要作用。本文着重考察了EMIM 和PF6-相互作用的三种氢键方式。     

Computational materials design: A perspective for atomistic approaches

Summary Present theoretical and computational approaches, combined with the impressive advances in computer hardware and software, open the possibility for materials design from first principles. This article presents a perspective on the relevant developments in computational chemistry, solid state physics and statistical mechanics and it assesses the merits and limitations of Hartree-Fock, density functional, semiempirical and force field approaches in terms of six criteria: capability, generality, accuracy, accessible system size, accessible time scales and computational efficiency. Functional materials for microelectronic, optical and magnetic applications currently present better opportunities for first-principles approaches than structural materials, where atomistic approaches, despite some encouraging results, are still far from capturing the full complexity of the dynamics involved in mechanical, thermal, diffusive and corrosive behavior.     

Selective oxidation of methane by dinitrogen monoxide on FeZSM-5 zeolites. Ab initio quantum chemical analysis

On the basis of ab initio quantum chemical calculations, we propose the structure and energetics of the species taking part in the selective oxidation of methane by dinitrogen monoxide on FeZSM-5 zeolites. The immediate oxidizing site is reasonably represented by a binuclear iron-hydroxide cluster with a peroxo-like fragment located between iron atoms.     

A general purpose Fortran 90 electronic structure program for conjugated systems using Pariser-Parr-Pople model

Pariser-Parr-Pople (P-P-P) model Hamiltonian has been used extensively over the years to perform calculations of electronic structure and optical properties of π-conjugated systems successfully. In spite of tremendous successes of ab initio theory of electronic structure of large systems, the P-P-P model continues to be a popular one because of a recent resurgence in interest in the physics of π-conjugated polymers, fullerenes and other carbon-based materials. In this paper, we describe a Fortran 90 computer program developed by us, which uses P-P-P model Hamiltonian to not only solve Hartree-Fock (HF) equation for closed- and open-shell systems, but also for performing correlation calculations at the level of single configuration interactions (SCI) for molecular systems. Moreover, the code is capable of computing linear optical absorption spectrum at various levels, such as, tight-binding (TB) Hückel model, HF, SCI, and also of calculating the band structure using the Hückel model. The code also allows the user to solve the HF equation in the presence of finite external electric field, thus, permitting calculations of quantities such as static polarizabilities and electro-absorption spectra. Additionally, it can perform transformation of P-P-P model Hamiltonian from the atomic orbital (AO) representation (also called site representation) to the molecular orbital (MO) one, so that the transformed matrix elements can be used for high level post-HF calculations, such as, full CI (FCI), quadruple CI (QCI), and multi-reference singles-doubles CI (MRSDCI). We demonstrate the capabilities of our code by performing calculations of various properties on conjugated systems such as trans-polyacetylene (t-PA), poly-para-phenylene (PPP), poly-para-phenylene-vinylene (PPV), oligo-acenes, and graphene nanodisks.

Program summary

Program title: ppp.xCatalogue identifier: AEFW_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFW_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 79 900No. of bytes in distributed program, including test data, etc.: 508 285Distribution format: tar.gzProgramming language: Fortran 90. Compilers used: Program has been tested with Intel Fortran Compiler (noncommercial version 11.1) and gfortran compiler (gcc version 4.4.0) with optimization option -OComputer: PCs, workstationsOperating system: Linux. Code was developed and tested on various recent versions of Fedora including Fedora 11 (kernel version 2.6.29.4-167)Classification: 7.3, 16.1External routines: This program needs to link with LAPACK/BLAS libraries compiled with the same compiler as the program. For the Intel Fortran Compiler we used the ACML library version 4.3.0, while for gfortran compiler we used the libraries supplied with the Fedora distribution.Nature of problem: The problem of interest at hand is the electronic structure of π-conjugated systems. For such systems, the effective π-electron P-P-P semi-empirical model Hamiltonian proposed by Pariser, Parr, and Pople offers an attractive alternative as compared to the ab initio approaches. The present program can solve the HF equations for both open- and closed-shell systems within the P-P-P model. Moreover, it can also include electron correlation effects at the singles CI level. Along with the wave functions and energies, various properties such as linear absorption spectra can also be computed.Solution method: The single-particle HF orbitals of a π-conjugated system are expressed as linear combinations of the pz-orbitals of individual atoms (assuming that the system is in the xy-plane). Then using the hopping and Coulomb parameters prescribed for the P-P-P method, the HF integro-differential equations are transformed into a matrix eigenvalue problem. Thereby, its solutions are obtained in a self-consistent manner, using the iterative diagonalizing technique. The HF orbitals thus obtained can be used to perform a variety of calculations such as the SCI, linear optical absorption spectrum, polarizability, electro-absorption spectrum, etc.Running time: The examples provided each only take a few seconds to run. For a large molecule or a polymer, however, the run time may be a few minutes.     

树状分子聚酰胺胺(PAMAM)的量子化学研究

采用传统的Hartree-Fock(HF)从头算和密度泛函B3LYP方法,选择不同的基组水平(3-21G,6-31G*)对以乙二胺为核的1.0代PAMAM分子进行全几何优化,并对结果进行比较,同时与实验值进行对照.结果表明,B3LYP/6-31G*方法得到的结果更可靠.B3LYP/6.31G*计算结果表明,1.0代PAMAM分子构象不完全对称,4个支链基本在一个平面上,伯胺,仲胺和叔胺上的N原子所带负电荷数逐渐减少,HOMO轨道主要集中在核上,核极易发挥供电子作用.     

A program for computing weak and intermediate field Zeeman splittings from MCHF wave functions

Given electronic wave functions generated by the MCHF_CI program (LSJ format), this program calculates diagonal Landé g factors that determine separations of magnetic sublevels in weak external magnetic fields. In addition the program computes off-diagonal Landé g factors and constructs the total interaction matrix for an atom in a magnetic field. By diagonalizing the interaction matrix and plotting the eigenvalues as functions of the magnetic field, Zeeman structures beyond the weak field limit are obtained.     

A Theoretical Study on Nitrourea and its Tautomers

In the present study, nitrourea and its possible tautomers have been subjected to theoretical analysis by performing Hartree-Fock and also density functional theory (DFT) calculations. The optimized geometries, vibrational frequencies, and some thermodynamical values for the presently considered species have been obtained in their ground states.