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Full Wave Function Optimization with Quantum Monte CarloA Study of the Dissociation Energies of ZnO, FeO, FeH, and CrS
journal contribution
posted on 2019-09-04, 17:38 authored by Jil Ludovicy, Kaveh Haghighi Mood, Arne LüchowThe
dissociation energies of four transition-metal dimers are determined
using diffusion Monte Carlo. The Jastrow, configuration interaction,
and molecular orbital parameters of the wave function are both partially
and fully optimized with respect to the variational energy. The pivotal
role is thereby ascribable to the optimization of the molecular orbital
parameters of a complete active space wave function in the presence
of a Jastrow correlation function. Excellent results are obtained
for ZnO, FeO, FeH, and CrS. In addition, potential energy curves are
computed for the first three compounds at the multireference diffusion
Monte Carlo (MR-DMC) level, from which spectroscopic constants such
as the equilibrium bond distance, the harmonic frequency, and the
anharmonicity are extracted. All of these quantities agree well with
the experiment. Furthermore, it is shown for CrS that a restricted
active space calculation can yield improved initial orbitals by including
single and double excitations from the original active space into
a set of virtual orbitals. We demonstrated in this study that the
fixed-node error in DMC can be systematically reduced for multireference
systems by orbital optimization in compact active spaces. Although
DMC calculations with a large number of determinants are possible
and very accurate, our results demonstrate that compact wave functions
may be sufficient in order to obtain accurate nodal surfaces, which
determine the accuracy of DMC, even in the case of transition-metal
compounds.
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Jastrow correlation functionnodal surfacesoptimizationCrSDMC calculationswave functionsDissociation Energiesmultireference diffusion Monte Carloconfiguration interactionFull Wave Function OptimizationExcellent resultstransition-metal dimersdiffusion Monte CarloZnOfixed-node errorFeOtransition-metal compoundsFeHmultireference systemsvariational energyMR-DMCspace calculationdissociation energiesspace wave functionparameterorbitalequilibrium bond distancespectroscopic constantsenergy curveswave function
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