Calculation of Wannier centers and spreads

[iskarmou]

Dear all,

I am simulating a mixture of H2O-CO2 and after
an equilibration period of 4 ps I am performing
a productive run to calculate the system properties.
Among these properties, I want to calculate
Wannier centers and spreads.
I am using the following method (I attach the corresponding part of the input file):

     &LOCALIZE

     METHOD CRAZY
     EPS_LOCALIZATION 1.0E-8

     &PRINT
        &WANNIER_CENTERS
          &EACH
            MD 1
          &END EACH
          IONS+CENTERS T
          FORMAT XMOL
          FILENAME ./ions+centers.xyz
          COMMON_ITERATION_LEVELS               3
        &END WANNIER_CENTERS

        &WANNIER_SPREADS
          &EACH
            MD 1
          &END EACH
          FILENAME ./wannier-spreads
          COMMON_ITERATION_LEVELS               3
        &END WANNIER_SPREADS

      &END PRINT
    &END LOCALIZE

However, the run is significantly slower in comparison with the
previous runs, when I was not calculating Wannier centers and spreads.
Is there any way, from a methodology and technical point (eg parameter choice) of view, to speed up my calculation
without losing the accuracy in the estimation of the Wannier centers?

Thanks in advance

Yannis Skarmoutsos

[Marcella Iannuzzi]

Dear Yannis, 

Probably the localisation algorithm requires many iterations to converge.

Are you sure that you need such a tight convergence for EPS_LOCALIZATION?

Did you check whether a less tight value really affects the results?

You can try to replace CRAZY with JACOBI, maybe it converges faster. 

regards

Marcella

[iskarmou]

Dear Marcella,

thanks for your reply.
I tried the Jacobi algorithm as well and I have
seen that in general less iterations were required (with the
same tight convergence).
However the convergence parameter, as you say, is too tight.
The reason I used this value is not really based upon strong scientific
arguments, it's because I have seen several people using tight criteria.
Regarding the effect of convergence parameters on the results, which thing do you think that it would
be the most appropriate to check?
Should I calculate eg the dipoles from the Wannier ions_center trajectory file using different convergence criteria?
Or the spreads as well?
Is there another way to check this effect?
And do you know if there is any "optimum" value for the convergence parameter for these kind of systems?

Best regards

Yannis

[Marcella Iannuzzi]

Dear Yannis,

The molecular dipoles are a good quantity to check.

ciao

Marcella