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The electronic structure of an atom or molecule is the quantum state of its electrons. [13] The first step in solving a quantum chemical problem is usually solving the Schrödinger equation (or Dirac equation in relativistic quantum chemistry ) with the electronic molecular Hamiltonian , usually making use of the Born–Oppenheimer (B–O ...
Ab initio quantum chemistry methods are a class of computational chemistry techniques based on quantum chemistry that aim to solve the electronic Schrödinger equation. [1] Ab initio means "from first principles" or "from the beginning", meaning using only physical constants [2] and the positions and number of electrons in the system as input.
Density functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body systems, in particular atoms, molecules, and the condensed phases.
The Kohn–Sham electronic structure must not be confused with the real, quasiparticle electronic structure of a system, and there is no Koopmans' theorem holding for Kohn–Sham energies, as there is for Hartree–Fock energies, which can be truly considered as an approximation for quasiparticle energies. Hence, in principle, Kohn–Sham based ...
They can be used to relate molecular orbital calculations to simple bonding theories, and also to speed up post-Hartree–Fock electronic structure calculations by taking advantage of the local nature of electron correlation. Localized orbitals in systems with periodic boundary conditions are known as Wannier functions.
This leads to the determination of more accurate structures and electronic properties, or in the case of ab initio methods, to somewhat faster convergence. The method was first used by Roald Hoffmann who developed, with Robert Burns Woodward, rules for elucidating reaction mechanisms (the Woodward–Hoffmann rules). He used pictures of the ...
Such a calculation in the Gaussian and Spartan programs also give the MP2 and MP4 energies which are also used. The effect of polarization functions is assessed using an MP4 calculation with the 6-311G(2df,p) basis set. The effect of diffuse functions is assessed using an MP4 calculation with the 6-311+G(d, p) basis set.
This book contains predicted electron configurations for the elements up to 172, as well as 184, based on relativistic Dirac–Fock calculations by B. Fricke in Fricke, B. (1975). Dunitz, J. D. (ed.). "Superheavy elements a prediction of their chemical and physical properties". Structure and Bonding. 21. Berlin: Springer-Verlag: 89– 144.