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Abstract
We study the efficiency, precision and accuracy of all-electron variational and diffusion
quantum Monte Carlo calculations using Slater basis sets. Starting from wave functions
generated by Hartree-Fock and density functional theory, we describe an algorithm
to enforce the electron-nucleus cusp condition by linear projection. For the 55 molecules
in the G2 set, the diffusion quantum Monte Carlo calculations recovers an average
of 95% of the correlation energy and reproduces bond energies to a mean absolute deviation
of 3.2 kcal/mol. Comparing the individual total energies with essentially exact values,
we investigate the error cancellation in atomization and chemical reaction path energies,
giving additional insight into the sizes of nodal surface errors.