Ryan_Hunt wrote:Vladimir,

I'm not sure what you are asking here. You're ground state energy is: -109.542(1) a.u., whilst the exact value (from Ref. 38 of the quoted PRE article) is -109.5421 a.u. These two are consistent with each other (at the level of statistical significance you are working), and your VMC energy is slightly higher (-109.468(3) a.u.), which is to be expected.

If you do go ahead and reduce your DMC error bar to investigate further, be aware that population control bias and time step bias may muddy your comparison to the exact energy (in principle you should extrapolate data from two or more DMC simulations to remove these biases - see the paper here

https://link.aps.org/doi/10.1103/PhysRevE.83.066706 for some best practices). Your attached input files relate to a DMC calculation at /one/ time step and at /one/ population size, therefore you shouldn't necessarily expect to reproduce the exact energy very well.

Regards,

Ryan.

Hello Rian.

Initially, I was conducting calculations with 5 determinant WFN obtained from QChem VOD and of course I did calculations for different time steps and populations:

dtdmc: 0.0034; configurations = 1024; E = -109.545857117528 +/- 0.000705444506

dtdmc: 0.0011; configurations = 1024; E = -109.547862314555 +/- 0.000929138775

dtdmc: 0.0034; configurations = 3092; E = -109.546467643406 +/- 0.000787726772

From this we see that even linear extrapolation to zero timestep and infinity population leads to unreasonable, better then exact results.

I can perform there calculations for single determinant but while the best ever SD DMC is -109.5060(7), my SD DMC results is -109.541(1) and I don't think that time step and population biases are so great in my case, to disregard this difference.

Time step and population bias for 5 determinant WFN is order of 0.01 Ha, so I expect they should be comparable in the SD case.

Best Vladimir.

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