Communication: Toward an improved control of the fixed-node error in quantum Monte Carlo: The case of the water molecule

Abstract

Iterative perturbation calculations of ground and excited state energies from multiconfigurational zeroth-order

A Mountaineering Strategy to Excited States: Highly Accurate Energies and Benchmarks for Medium Sized Molecules

“…The increase of computational ressources coupled to the emergence of more advanced algorithms has led to a resurgence of the selected configuration interaction (SCI) approaches [1][2][3] as an effective strategy to rapidly reach the full CI (FCI) limit at a fraction of the cost of a genuine FCI calculation thanks to a sparse exploration of the FCI space. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] This revival is especially beneficial for the calculation of transition energies between electronic states, 6,[15][16][17][18][19][20][21][22][23] as the accurate determination of these energies remains one of the great challenges faced by theoretical chemists.…”

Using CIPSI Nodes in Diffusion Monte Carlo

“…[1][2][3][4][5] The purpose of this paper is to review the present situation, to clarify some important aspects of DMC-CIPSI, and to present some new illustrative results.…”

Electron correlation by polarization of interacting densities

“…In He, for example, important correlation effects can be accomplished by the polarizations, ( ) Many very accurate configuration interaction calculations have been carried out on atoms, molecules and clusters using large basis sets that include higher spherical harmonic functions. [1][2][3][4][5][6][7][8][9][10][11] As systems increase in size, the additional functions required for angular correlation cause a rapid increase in the number of configurations, limiting the applicability of the method.…”

“…There is a vast literature on ways to do this ranging from perturbation methods that generate configurations and evaluate energies efficiently to methods for partitioning large systems into localized electronic subspaces or ways to balance errors in systems that are being compared. [1][2][3][4][5][6][7][8][9][10][11] Relatively few configurations are required to dissociate molecules correctly or to create proper spin states. However, dynamical correlation effects, particularly those associated with angular correlation, require higher spherical harmonic basis functions and this leads to a rapid increase in number of interacting configurations.…”