H4: A model system for assessing the performance of diffusion Monte Carlo calculations using a single Slater determinant trial function

• DOI: 10.1063/1.4986216
• Publication Date: 2017-08-15T13:09:33Z
• Authors: Kevin Gasperich; Michael Deible; Kenneth D. Jordan
• Keywords: Diradical; Slater determinant; Diffusion Monte Carlo; Square (algebra)

A model H4 system is used to investigate the accuracy of diffusion Monte Carlo (DMC) calculations employing a single Slater determinant fix nodal surface. The lowest energy singlet state square diradical which poorly described by DMC using (SD) trial function. Here we consider distortions rectangular structures, decrease amount character. falloff error in SD-DMC with increasing separation between two H2 molecules found be much more rapid for small away from than large distortions. This behavior shown correlated extent mixing configurations needed properly describe sizeable (∼0.1 eV) even separations at coefficient dominant configuration four-electron, four-orbital complete active space self-consistent-field wave function as 0.9.