  Calculations of the binding energy of the transition metal oxide molecules
TiO and MnO are presented, using a recently developed phaseless auxiliary field
quantum Monte Carlo approach. This method maps the interacting many-body
problem onto a linear combination of non-interacting problems by a complex
Hubbard-Stratonovich transformation, and controls the phase/sign problem with a
phaseless approximation relying on a trial wave function. It employs random
walks in Slater determinant space to project the ground state of the system,
and allows use of much of the same machinery as in standard density functional
theory calculations, such as planewave basis and non-local pseudopotentials.
The calculations used a single Slater determinant trial wave function obtained
from a density functional calculation, with no further optimization. The
calculated binding energies are in good agreement with experiment and with
recent diffusion Monte Carlo results. Together with previous results for
sp-bonded systems, the present study indicates that the phaseless auxiliary
field method is a robust and promising approach for the study of correlation
effects in real materials.
