Abstract
In this work, we present a simple decomposition scheme of the Kohn-Sham optimized orbitals which is able to provide a reduced basis set, made of localized polycentric orbitals, specifically designed for Quantum Monte Carlo. The decomposition follows a standard Density functional theory (DFT) calculation and is based on atomic connectivity and shell structure. The new orbitals are used to construct a compact correlated wave function of the Slater–Jastrow form which is optimized at the Variational Monte Carlo level and then used as the trial wave function for a final Diffusion Monte Carlo accurate energy calculation. We are able, in this way, to capture the basic information on the real system brought by the Kohn-Sham orbitals and use it for the calculation of the ground state energy within a strictly variational method. Here, we show test calculations performed on some small selected systems to assess the validity of the proposed approach in a molecular fragmentation, in the calculation of a barrier height of a chemical reaction and in the determination of intermolecular potentials. The final Diffusion Monte Carlo energies are in very good agreement with the best literature data within chemical accuracy.
Highlights
Density functional theory (DFT) is a quantum-mechanical approach mainly developed for the study of the electronic structure of many body systems like atoms, molecules and solids
A procedure to decompose the KS optimized orbitals with the aim of generating a new basis set designed for Quantum Monte Carlo (QMC) calculations is given
By starting from an accurate electron density, the procedure allows the construction of a correlated wave function that is further optimized within a step of VMC computation
Summary
Density functional theory (DFT) is a quantum-mechanical approach mainly developed for the study of the electronic structure of many body systems like atoms, molecules and solids. The Thomas-Fermi [1,2] statistical method laid the foundations of DFT but only with the Hohenberg-Kohn [3] theorems was this new method put on a firm theoretical footing. This approach is completely different from standard quantum-mechanical methodologies based on the calculation of an N particle wave function.
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