Simulating nonadiabatic effects with many-body wave function approaches is anopen field with many challenges. Recent interest has been driven by newalgorithmic developments and improved theoretical understanding of propertiesunique to electron-ion wave functions. Fixed-node diffusion Monte Caro is onetechnique that has shown promising results for simulating electron-ion systems.In particular, we focus on the CH molecule for which previous results suggesteda relatively significant contribution to the energy from nonadiabatic effects.We propose a new wave function ansatz for diatomic systems which involvesinterpolating the determinant coefficients calculated from configurationinteraction methods. We find this to be an improvement beyond previous wavefunction forms that have been considered. The calculated nonadiabaticcontribution to the energy in the CH molecule is reduced compared to ourprevious results, but still remains the largest among the molecules underconsideration.
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