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Evaluation of Finite size effects #2000
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I forgot to mention: |
I think that @jtkrogel has the best perspective of the situation but he is out for a few days. When he is back and has time we should discuss the situation here. Clearly MPC need to work since it is a standard (default?) observable for solid state calculations. I see two issues (1) How are the results output and analysed conveniently, including with error cancelation as mentioned above? Some tweaks to qmca could handle this. (2) What is the status of MPC in the main develop branch, what is tested etc.? This is important given the upcoming transition to a single code path. |
Currently I was actually unaware of (or had forgotton) the Chiesa S(k) breakage in SoA. It is clearly not implemented however. This is important enough to add it to the list for the SoA transition, though I don't know who would do the implementation. I will add it to the list in #861 and discussion can follow here or there. I expect v3.7.0 AoS should be OK; @ye-luo should comment here otherwise. The |
@zenandrea see #2026 for the |
@jtkrogel I think @Paul-St-Young is the current expert on the status of this tool. |
@jtkrogel many thanks. A possible fix to that is to change the line 1851 of qmca into Maybe the most general solution would be to allow qmca to evaluate an expression given as input, |
@zenandrea I think I have a fix that will capture all the situations you describe. Please try out the updated code in #2042 and let me know if it works. Expression evaluation is an intriguing idea. Since this breaks the mold a bit, I will let this wait until after adequate test code has been made for qmca (tests should all be present by end Nov). |
@jtkrogel Awesome, it works in my systems. |
I would like to evaluate finite size effects.
Concerning the correction to the potential, I can use MPC.
If I set in input
<pairpot name="ElecElec" type="coulomb" source="e" target="e" /> <pairpot type="MPC" name="MPC" source="e" target="e" ecut="30.0" physical="no"/>
then the local energy is calculated using the Ewald ElecElec interaction.
The correction is given my MPC-ElecElec.
I can use the tool qmca to have the value and associated error of MPC and ElecElec, separately, but not of the difference (which would have a much smaller error, because of the correlation between the MPC and ElecElec fluctuations).
So, if I want to compute the MPC-ElecElec error I should write a script to do that.
Am I correct? Or is there some way to tell qmca or some other script to do that?
Concerning the kinetic correction:
As far as I understood, I cannot get the kinetic correction or the structure factor from the SoA version, because it not yet implemented. Thus, I should instead use the AoS version (which could have a bug in version v.3.8.0, issue #1995).
Which version of qmcpack is safe for those quantities (v.3.7.0 AoS)?
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