Quantum Monte Carlo calculations of NiO

We describe variational and diffusion quantum Monte Carlo (VMC and DMC) calculations [1] of NiO using a 1024-electron simulation cell. We have used a smooth, norm-conserving, Dirac-Fock pseudopotential [2] in our work. Our trial wave functions were of Slater-Jastrow form, containing orbitals generated in Gaussian-basis UHF periodic calculations. Jastrow factor is optimized using variance minimization with optimized cutoff lengths using the same scheme as our previous work. [4] We apply the lattice regulated scheme [5] to evaluate non-local pseudopotentials in DMC and find the scheme improves the smoothness of the energy-volume curve. \newline \newline [1] CASINO ver.2.1 User Manual, University of Cambridge (2007). \newline [2] J.R. Trail {\it et.al.}, J. Chem. Phys. {\bf 122}, 014112 (2005). \newline [3] CRYSTAL98 User's Manual, University of Torino (1998). \newline [4] Ryo Maezono {\it et.al.}, Phys. Rev. Lett., {\bf 98}, 025701 (2007). \newline [5] Michele Casula, Phys. Rev. B {\bf 74}, 161102R (2006).