[CPMD-list] Energy components in PIMD

[Łukasz Walewski]

Dnia 29-04-2008, Wt o godzinie 12:57 -0400, Axel Kohlmeyer pisze:
> On Tue, 29 Apr 2008, ukasz Walewski wrote:
> 
> dear lukasz,
> 
> LW> Oh, yes! I forgot to mention: of course I did the CPMD (non-PIMD) NVE
> LW> (http://bioexploratorium.pl/ljw/cpmd/nve/) and NVT
> LW> (http://bioexploratorium.pl/ljw/cpmd/nvt/) test simulations (input files
> LW> together with the plots).
> 
> did you do those in sequence? all your NVT inputs don't read 
> in the velocities from the previous runs. if you have your 
> system already working in CP-dynamics, you don't want to 
> "rock the boat" but with each restart and re-initializing of 
> the velocities you do exactly that and get further away from 
> the BO-surface.

No, I did not. I did the NVT runs independently from NVE ones (i.e.
optimizing wavefunction from scratch). I agree it would be wiser to take
advantage of previous runs and restart NVT from the NVE and turn the
thermostat on. I have run them in parallel however...

> and from the NVT run you can see that your fictitous dynamics
> is picking up significant energy (at what length of timestep?
> 1.0 a.u.?) so there is something fishy going on. so as i was

No, at dt = 4.0 a.u.

> implying in my previous mail. the NVE runs work by accident
> since you don't excite all DOFs. the massive ion thermosts
> will enforce equipartitioning and takes that away and thus
> creates some lack of adiabacity. in my experience with USPPs
> the can be somewhat alleviated by increasing the density cutoff,
> but that comes at a performance and memory penalty that usually
> makes norm-conserving potentials somewhat competetive (and much
> less of a hassle to boot. if you had any elements that were
> "difficult" and are better represented by USPPs it would make
> more sense...).

[...]

> so i would suggest you repeat the NVE tests (and NVT without 
> a thermostat on the electrons) with a DUAL of 6, 8 and 10
> and see if that improves the situation and to what degree.

Perhaps I can skip the NVE tests, since the runs I did already do not
show any suspicious behavior (accidentally, as you said). What went
wrong was the NVT run. What do you think ?

> i would also do one test with norm conserving potentials to
> see how they compare.
> 
> good luck!

Thanks a lot for this valuable discussion and suggestions.

Kind regards,
Lukasz