|
Valence Bond Programs
Valence bond (VB) computer programs for modern valence bond calculations:- * CRUNCH, by Gordon A. Gallup and his group. * GAMESS (UK), includes calculation of VB wave functions by the TURTLE code, due to J.H. van Lenthe. * GAMESS (US), has links to interface VB2000, and XMVB. * MOLPRO and MOLCAS include code by David L. Cooper for generating Spin Coupled VB wave functions from CASSCF calculations. * VB2000 version 2.7 (released, 2014), by Jiabo Li, Brian Duke and Roy McWeeny allows the use of Group Function theory, whereby different groups can be handled by different methods (VB or Hartree–Fock). Many types of VB, including spin-coupled VB, and CASVB calculations are possible. It is part of the GAMESS (US) release and can be compiled into the GAMESS(US) executable. There is a more limited stand-alone program. Earlier versions were interfaced to GAUSSIAN. * XMVB (previously known as XIAMEN), by Lingchun Song, Yirong Mo, Qianer Zhang and Wei Wu. This allows several VB methods, i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modern Valence Bond Theory
Modern valence bond theory is the application of valence bond theory VBT with computer programs that are competitive in accuracy and economy with programs for the Hartree–Fock or post-Hartree-Fock methods. The latter methods dominated quantum chemistry from the advent of digital computers because they were easier to program. The early popularity of valence bond methods thus declined. It is only recently that the programming of valence bond methods has improved. These developments are due to and described by Gerratt, Cooper, Karadakov and Raimondi (1997); Li and McWeeny (2002); Joop H. van Lenthe and co-workers (2002); Song, Mo, Zhang and Wu (2005); and Shaik and Hiberty (2004) While Molecular Orbital Theory OTdescribes the electronic wavefunction as a linear combination of basis functions that are centered on the various atoms in a species (Linear combination of atomic orbitals), VBT describes the electronic wavefunction as a linear combination of several valence bond struct ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GAMESS (UK)
General Atomic and Molecular Electronic Structure System (GAMESS-UK) is a computer software program for computational chemistry. The original code split in 1981 into GAMESS-UK and GAMESS (US) variants, which now differ significantly. Many of the early developments in the UK version arose from the earlier UK based ATMOL program, which, unlike GAMESS, lacked analytical gradients for geometry optimisation. GAMESS-UK can perform many general computational chemistry calculations, including Hartree–Fock method, Møller–Plesset perturbation theory (MP2 & MP3), coupled cluster (CCSD & CCSD(T)), density functional theory (DFT), configuration interaction (CI), and other advanced electronic structure methods. Calculation of valence bond wave functions are possible by the TURTLE code, due to J. H. van Lenthe. See also * CP2K * GAMESS (US) * Gaussian (software) * MOLCAS * MOLPRO * MPQC * NWChem * PSI (computational chemistry) (Psi3) * Firefly (computer program) * Q-Chem * Quantum chemistr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wave Function
A wave function in quantum physics is a mathematical description of the quantum state of an isolated quantum system. The wave function is a complex-valued probability amplitude, and the probabilities for the possible results of measurements made on the system can be derived from it. The most common symbols for a wave function are the Greek letters and (lower-case and capital psi, respectively). The wave function is a function of the degrees of freedom corresponding to some maximal set of commuting observables. Once such a representation is chosen, the wave function can be derived from the quantum state. For a given system, the choice of which commuting degrees of freedom to use is not unique, and correspondingly the domain of the wave function is also not unique. For instance, it may be taken to be a function of all the position coordinates of the particles over position space, or the momenta of all the particles over momentum space; the two are related by a Fourier tran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GAMESS (US)
General Atomic and Molecular Electronic Structure System (GAMESS (US)) is computer software for computational chemistry program. The original code started on October 1, 1977 as a National Resources for Computations in Chemistry project. In 1981, the code base split into GAMESS (US) and GAMESS (UK) variants, which now differ significantly. GAMESS (US) is maintained by the members of the Gordon Research Group at Iowa State University. GAMESS (US) source code is available as source-available freeware, but is not open-source software, due to license restrictions. Abilities GAMESS (US) can perform several general computational chemistry calculations, including Hartree–Fock method, density functional theory (DFT), generalized valence bond (GVB), and multi-configurational self-consistent field (MCSCF). Correlation corrections after these SCF calculations can be estimated by configuration interaction (CI), second order Møller–Plesset perturbation theory (MP2), and coupled clust ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MOLPRO
MOLPRO is a software package used for accurate ''ab initio'' quantum chemistry calculations. It is developed by Peter Knowles at Cardiff University and Hans-Joachim Werner at Universität Stuttgart in collaboration with other authors. The emphasis in the program is on highly accurate computations, with extensive treatment of the electron correlation problem through the multireference configuration interaction, coupled cluster and associated methods. Integral-direct local electron correlation methods reduce the increase of the computational cost with molecular size. Accurate ab initio calculations can then be performed for larger molecules. With new explicitly correlated methods the basis set limit can be very closely approached. History Molpro was designed and maintained by Wilfried Meyer and Peter Pulay Peter Pulay (born September 20, 1941, in Veszprém, Hungary) is a theoretical chemist. He is the Roger B. Bost Distinguished Professor of Chemistry in the Department of Chemis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MOLCAS
MOLCAS is an ab initio computational chemistry program, developed as a joint project by a number of international institutes. MOLCAS is developed by scientists to be used by scientists. It is not primarily a commercial product and it is not sold in order to produce a fortune for its owner (the Lund University). Focus in the program is placed on methods for calculating general electronic structures in both ground and excited states. MOLCAS contains codes for general and effective multiconfigurational SCF calculations at the Complete Active Space (CASSCF) level, but also employing more restricted MCSCF wave functions (RASSCF). It is also possible, at this level of theory, to optimize geometries for equilibrium and transition states using gradient techniques and to compute force fields and vibrational energies. MOLCAS also contains second order perturbation theory codes CASPT2 and RASPT2. History MOLCAS code has been created at the late 1980s by the group of Prof. Björn O. R ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multi-configurational Self-consistent Field
Multi-configurational self-consistent field (MCSCF) is a method in quantum chemistry used to generate qualitatively correct reference states of molecules in cases where Hartree–Fock and density functional theory are not adequate (e.g., for molecular ground states which are quasi-degenerate with low-lying excited states or in bond-breaking situations). It uses a linear combination of configuration state functions (CSF), or configuration determinants, to approximate the exact electronic wavefunction of an atom or molecule. In an MCSCF calculation, the set of coefficients of both the CSFs or determinants and the basis functions in the molecular orbitals are varied to obtain the total electronic wavefunction with the lowest possible energy. This method can be considered a combination between configuration interaction (where the molecular orbitals are not varied but the expansion of the wave function) and Hartree–Fock (where there is only one determinant, but the molecular orbitals ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Roy McWeeny
Roy McWeeny (19 May 1924 – 29 April 2021) was a British academic physicist and chemist. McWeeny was born in Bradford, Yorkshire in May 1924. His first degree was in physics from the University of Leeds. He then obtained a D.Phil. in mathematical physics and quantum theory under the supervision of Charles Coulson at the Mathematical Institute, University of Oxford. From 1948 to 1957 he was lecturer in physical chemistry at King's College, University of Durham (King's College is now the University of Newcastle upon Tyne). From 1957 to 1965 he was at the University of Keele rising to Professor of Theoretical Physics and Theoretical Chemistry. From 1966 to 1982 he was Professor of Theoretical Chemistry at the University of Sheffield. In 1982 he moved to the University of Pisa, Italy where he remained an Emeritus Professor until his death. In 1996 a celebratory ''festschrift'' volume was published in his honour containing original papers by 132 scientists from 19 countries. He was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hartree–Fock Method
In computational physics and chemistry, the Hartree–Fock (HF) method is a method of approximation for the determination of the wave function and the energy of a quantum many-body system in a stationary state. The Hartree–Fock method often assumes that the exact ''N''-body wave function of the system can be approximated by a single Slater determinant (in the case where the particles are fermions) or by a single permanent (in the case of bosons) of ''N'' spin-orbitals. By invoking the variational method, one can derive a set of ''N''-coupled equations for the ''N'' spin orbitals. A solution of these equations yields the Hartree–Fock wave function and energy of the system. Especially in the older literature, the Hartree–Fock method is also called the self-consistent field method (SCF). In deriving what is now called the Hartree equation as an approximate solution of the Schrödinger equation, Hartree required the final field as computed from the charge distribution to be "s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
William A
William is a male given name of Germanic origin.Hanks, Hardcastle and Hodges, ''Oxford Dictionary of First Names'', Oxford University Press, 2nd edition, , p. 276. It became very popular in the English language after the Norman conquest of England in 1066,All Things William"Meaning & Origin of the Name"/ref> and remained so throughout the Middle Ages and into the modern era. It is sometimes abbreviated "Wm." Shortened familiar versions in English include Will, Wills, Willy, Willie, Bill, and Billy. A common Irish form is Liam. Scottish diminutives include Wull, Willie or Wullie (as in Oor Wullie or the play ''Douglas''). Female forms are Willa, Willemina, Wilma and Wilhelmina. Etymology William is related to the given name ''Wilhelm'' (cf. Proto-Germanic ᚹᛁᛚᛃᚨᚺᛖᛚᛗᚨᛉ, ''*Wiljahelmaz'' > German ''Wilhelm'' and Old Norse ᚢᛁᛚᛋᛅᚼᛅᛚᛘᛅᛋ, ''Vilhjálmr''). By regular sound changes, the native, inherited English form of the name shoul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Generalized Valence Bond
The generalized valence bond (GVB) is a method in valence bond theory that uses flexible orbitals in the general way used by modern valence bond theory. The method was developed by the group of William A. Goddard, III around 1970. Theory The generalized Coulson–Fischer theory for the hydrogen molecule, discussed in Modern valence bond theory, is used to describe every electron pair in a molecule. The orbitals for each electron pair are expanded in terms of the full basis set and are non-orthogonal. Orbitals from different pairs are forced to be orthogonal - the strong orthogonality condition. This condition simplifies the calculation but can lead to some difficulties. Calculations GVB code in some programs, particularly GAMESS (US) General Atomic and Molecular Electronic Structure System (GAMESS (US)) is computer software for computational chemistry program. The original code started on October 1, 1977 as a National Resources for Computations in Chemistry project. In 1981, t . ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Chemistry Computer Programs
Quantum chemistry computer programs are used in computational chemistry to implement the methods of quantum chemistry. Most include the Hartree–Fock (HF) and some post-Hartree–Fock methods. They may also include density functional theory (DFT), molecular mechanics or semi-empirical quantum chemistry methods. The programs include both open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized sof ... and commercial software. Most of them are large, often containing several separate programs, and have been developed over many years. Overview The following tables illustrates some of the main capabilities of notable packages: Numerical details Quantum chemistry and solid-state physics characteristics Post processing packages in quantum chemistry and solid-state physics ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
