Pairing wavefunctions, or how to improve (or not) nodal surfaces in
diffusion Monte-Carlo

Pascal Bugnion, Wed May 9th

Diffusion Monte-Carlo projects out the ground state wavefunction of a set of
Fermions. The solution is exact, apart from the "fixed node error" which
arises from the need to constrain the wavefunction to remain anti-symmetric.
Improving the nodal surface of the trial wavefunction leads to a decrease in
the fixed node error, and hence an improvement in the predictions of the DMC
algorithm. Several schemes have been proposed to improve the quality of the
trial wavefunctions, one of which involves using pairing functions [1]. We
will discuss the effect and effectiveness of pairing functions on the DMC
algorithm.

[1] Geminal wave functions with Jastrow correlation: A first application to
atoms, Casula and Sorella, J. Chem. Phys. 119, 6500 (2003).