Theory and software for large Quantum Monte Carlo super-computer simulations over exponential type orbitals.

Abstract

Slater‐type orbitals (STO) are rarely used as atomic basis sets for molecular structure and property calculations, since integrals are expensive to evaluate, reliable basis sets are scarce and exact properties such as Kato’s cusp condition and the correct exponential decay of the electron density are not significantly better described numerically than with commonly used Gaussian basis sets. We adopt the systematic parallelized development of integration routines for multi‐centre integrals, and high‐quality basis sets over STOs, useful for modern electron correlation calculations via compact low‐variance trial wave‐functions for QMC (Quantum Monte Carlo). Molecular QMC applications are also rare, because the method is comparatively complicated to use, however it is extremely precise and can be made to include nearly all the correlation energy. It also scales well for large numbers of processors (1000 s at nearly 100 percent efficiency). Applications need to be carried out on a large scale, to determine electronic structure and properties of large (about 100 atoms) molecules of chemical interest, including intermolecular interactions, best described using Slater trial wave‐functions for QMC. Such functions combined as hydrogen‐like atomic orbitals possess the correct nodal structure for the high precision FN‐MC (Fixed Node Monte Carlo) methods, which include more than 95 percent of the electron correlation energy.