title: Approaching chemical accuracy with quantum Monte Carlo.
abstract: A quantum Monte Carlo study of the atomization energies for the G2 set of molecules is presented. Basis size dependence of diffusion Monte Carlo atomization energies is studied with a single determinant Slater-Jastrow trial wavefunction formed from Hartree-Fock orbitals. With the largest basis set, the mean absolute deviation from experimental atomization energies for the G2 set is 3.0 kcal/mol. Optimizing the orbitals within variational Monte Carlo improves the agreement between diffusion Monte Carlo and experiment, reducing the mean absolute deviation to 2.1 kcal/mol. Moving beyond a single determinant Slater-Jastrow trial wavefunction, diffusion Monte Carlo with a small complete active space Slater-Jastrow trial wavefunction results in near chemical accuracy. In this case, the mean absolute deviation from experimental atomization energies is 1.2 kcal/mol. It is shown from calculations on systems containing phosphorus that the accuracy can be further improved by employing a larger active space.
authors.affiliation: Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA. frp3@cornell.edu
authors.forename: F R
authors.initials: FR
authors.lastname: Petruzielo
authors.forename: Julien
authors.initials: J
authors.lastname: Toulouse
authors.forename: C J
authors.initials: CJ
authors.lastname: Umrigar