spin symmetry in the Jastrow factor

[Alan_Todd_Yeates]

I am performing a vmc_opt calculation on benzene in which I set uu/=dd/=ud in U and F and u/=d in Chi. This appears to give a considerably better energy than uu=dd and u=d. I am concerned that since this is analogous to a spin unrestricted wavefunction, there might be spin contamination present. Is this a real concern, or will the dmc restore spin symmetry? If it is a concern, how do I determine if there is spin contamination and can I project it out?

[Neil Drummond]

Dear Alan,

I would have expect the "spin-polarised" wave function to be in principle just as good as the non-spin-polarised wave function. In practice it would be slightly more difficult to optimise the redundant parameters.

So I think something must be wrong in the case you describe, but I don't have enough information to say more.

Best wishes,

Neil.

[Vladimir_Konjkov]

I am performing a vmc_opt calculation on benzene in which I set uu/=dd/=ud in U and F and u/=d in Chi. This appears to give a considerably better energy than uu=dd and u=d. I am concerned that since this is analogous to a spin unrestricted wavefunction, there might be spin contamination present. Is this a real concern, or will the dmc restore spin symmetry? If it is a concern, how do I determine if there is spin contamination and can I project it out?

Hello Alan

Look this article https://aip.scitation.org/doi/10.1063/1.476330 there are some clues about spin contamination, so I don`t think that FN-DMC exactly restores spin symmetry but maybe it just reduces the already small value of spin contamination if present.

Best.

[Vladimir_Konjkov]

Hello Alan

Could you please provide your VMC energies for benzene to compare with those presented in the https://www.ncbi.nlm.nih.gov/pubmed/25725716 (TABLE VII)
Despite the fact that in this work totally symmetric Jastrow factor with respect to electron permutations was proposed, VMC energies for H2O and N2 are comparable to that from JASTROW of Pablo López-Ríos (CASINO) implementation.
It would be surprising if benzene was special in this regard.

Best Vladimir.