  We here apply the recently developed initiator density matrix quantum Monte
Carlo (i-DMQMC) to a wide range of chemical environments using atoms and
molecules in vacuum. i-DMQMC samples the exact density matrix of a Hamiltonian
at finite temperature and combines the accuracy of full configuration
interaction quantum Monte Carlo (FCIQMC) - full configuration interaction (FCI)
or exact energies in a finite basis set - with finite temperature. By way of
exploring the applicability of i-DMQMC for molecular systems, we choose to
study a recently developed test set by Rubenstein and coworkers: Be, H2O, and
H10 at near-equilibrium and stretched geometries. We find that, for Be and H2O,
i-DMQMC delivers energies which are sub-millihartree accuracy when compared
with finite temperature FCI. For H2O and both geometries of H10 we examine the
difference between FT-AFQMC and i-DMQMC which in turn is an estimate of the
difference in canonical versus grand canonical energies. We close with a
discussion of simulation parameters (initiator error and different basis sets)
and by showing energy difference calculations in the form of specific heat
capacity and ionization potential calculations.
