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Ab initio correlation functionals from second-order perturbation theory
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DOI：10.1063/1.2212936.png)
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Abstract
En 中文
Orbital-dependent exchange-correlation functionals are not limited by the explicit dependence on the density and present an attractive alternative to conventional functionals. With the successful implementation of the exact orbital-dependent exchange functional, the challenge lies in developing orbital-dependent approximations for the correlation functional. Ab initio many-body methods can provide such approximations. In particular, perturbation theory with the Kohn-Sham model as the reference [Gorling and Levy, Phys. Rev. A 50, 196 (1994)] defines the exact correlation functional via an infinite perturbation series. The second-order term of these series gives the lowest-order approximation to the correlation functional. However, it has been suggested [Bartlett , J. Chem. Phys. 122, 034104 (2005)] that the Kohn-Sham Hamiltonian is not the optimal choice for the perturbation expansion and a different reference Hamiltonian may lead to an improved perturbation series and more accurate second-order approximation. Here, we demonstrate explicitly that the modified series can be used to define superior functional and potential. We present results of atomic and molecular calculations with both second-order functionals. Our results demonstrate that the modified functional offers a significantly improved description of the correlation effects as it does not suffer from convergence problems and results in energies and densities that are more accurate than those obtained with second-order Moller-Plesset perturbation theory or generalized-gradient approximation functionals. (c) 2006 American Institute of Physics.
Keywords:
GENERALIZED GRADIENT APPROXIMATION
EXCHANGE-CORRELATION POTENTIALS
ORBITAL-DEPENDENT CORRELATION
MOLECULAR WAVE-FUNCTIONS
ANO BASIS-SETS
CORRELATION-ENERGY
HARTREE-FOCK
DENSITY
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