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Adaptive Quantum Monte Carlo Approach States for High-Dimensional Systems
Published in Xavier Oriols, Jordi Mompart, Applied Bohmian Mechanics, 2019
Eric R. Bittner, Donald J. Kouri, Sean Derrickson, Jeremy B. Maddox
The variational Monte Carlo (VMC) technique is a powerful way to estimate the ground state of a quantum mechanical system. The basic idea is that one can use the variational principle to minimize the energy expectation value with respect to a set of parameters {α} () E(α)=∫|ψ(x,α)|2(Hψ)/ψ(x,α))dx∫|ψ(x,α)|2dx.
Diffusion and reptation quantum Monte Carlo study of the NaK molecule
Published in Molecular Physics, 2019
Marc E. Segovia, Oscar N. Ventura
In this work we aimed to describe the bond length, dipole moment and dissociation energy of the NaK molecule from two complementary points of view. On one side, we performed DFT calculations (PBE0) with and without an empirical dispersion correction, as well as CCSD(T) calculations to study the PECs of NaK and some of its properties at equilibrium, in order to stablish the link between former theoretical calculations and our own. On the other side, we used three versions of the quantum Monte Carlo (QMC) method, namely Diffusion Monte Carlo (DMC), Reptation Monte Carlo (RMC) and Variational Monte Carlo (VMC) to study the NaK molecule ground state. The QMC calculations used trial wavefunctions calculated at the monoconfigurational (Hartree–Fock) and multiconfigurational (MCSCF and CISD) levels, as well as several DFT methods (B3LYP, PBE and BHHLYP). PECs, equilibrium distances, dipole moments and dissociation energies were calculated and compared both with experimental values and results from other theoretical calculations. The results show that the VMC calculations combined with DMC give a result for the dissociation energy (23.0 and 25.2 mhartrees at the CISD and CASSCF based QMC levels) not very far from the experimental result (about 4%). RMC is necessary however to improve the agreement of the calculated dipole moment with the experimental value. Systematic improvements in QMC are observed both when using multideterminant wavefunctions or fixed node approximations (FNA) corrections such as backflow. Possible deficiencies due to the use of pseudopotentials and small basis sets are discussed.