spin symmetry in the Jastrow factor

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spin symmetry in the Jastrow factor

Postby Alan_Todd_Yeates » Mon Aug 13, 2018 5:58 pm

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?
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Re: spin symmetry in the Jastrow factor

Postby Neil Drummond » Sun Oct 07, 2018 10:08 am

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.
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Re: spin symmetry in the Jastrow factor

Postby Vladimir_Konjkov » Tue Oct 23, 2018 3:52 am

Alan_Todd_Yeates wrote: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.
In Soviet Russia Casino play you.
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