[CP2K:8958] test of a new collective variable coded into CP2K

Dorothea Golze dorothe... at googlemail.com
Fri Apr 21 11:49:06 UTC 2017

Hi Sun,

I implemented a few colvars last year. I tested the derivatives simply my
finite differences. I wrote a subroutine for testing, that shifts each atom
(for each direction) by plus/minus a small delta. For each of the shifted
positions you can calculate your colvar. Do something like this:
    DO iparticle=1,SIZE(my_particles)
       dsdr_numerical = 0._dp
       DO dir=1,3
          DO shift=1,2
            std_value = my_particles(iparticle)%r(dir)
            my_particles(iparticle)%r(dir) = std_value - (-1.0_dp)**shift*dx
            Calculate colvar(shift)=....
           dsdr_numerical =0.5_dp*(colvar(1) - colvar(2))/dx

dsdr_numerical should correspond to what you calculated analytically.

Best regards,

2017-04-20 17:56 GMT+03:00 Sun Tao <taosun... at gmail.com>:

> Dear CP2K users/developers:
> I have coded a new collective variable into CP2K, in order to do some
> umbrella sampling. I have implemented the calculation of the CV's value and
> its derivative. The value is already tested and gives correct results.
> However, I am wondering how to test the correctness of the derivative,
> since this is essential if I want to do umbrella sampling simulations.
> If you have some experience in implementing CV's in CP2K, I would like to
> know how you tested the correctness of your implementation. I would
> appreciate if you could help me.
> Thanks ~
> Tao
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