[CPMD-list] serial and parallel gradients differ

[Ari P Seitsonen]

Dear Robert,

   'GEOMETRY STEP NR.   2284' - wow! The geometry of the system should have
converged MUCH, MUCH earlier. Maybe the reason is that you use the
Gauss-Hermite integration, did you check (e.g. in small molecules) that
the default values and pseudos are adequate? Especially the number of grid
points (the default value has been changed to '20' in the up-coming
versions of CPMD). The convergence 1.0e-6 is very tight for the ions, and
thus it has not been reached. My experience is also that the 'LBFGS'
algorithm (in section '&CPMD') converges usually very fast to the ground
state.

   Anyway, coming back to your actual question: The serial calculation has
been stopped because the default number of electronic iterations, 10000,
has been reached. So many steps shouldn't been necessary, it's usually a
sign of a problem during the calculation. Also the second calculation has
finished before all your convergence criterion for the forces has been
finished - I don't know why, but also here there is most likely some
problem in the input (if you send us the output we could give a look,
however 1400 geometry steps is MUCH too much also). If you definitely
want so accurate forces (of course very welcome e.g. when heading for
vibrational spectra), you could first check the Gauss-Hermit integration,
then try 'LBFGS'; but reaching 1.0e-6 might still be impossible.

     Greetings from rainy Paris,

        apsi

On Sat, 26 Mar 2005, Robert Williams wrote:

> Dear CPMDers,
>
> Results from my serial and parallel optimizations
> using cpmd3.9.1 differ significantly, starting from
> identical input files (attached) using tight
> convergence criteria.  Below are parts
> of the final results for serial and parallel runs
> on P4 linux systems.  Of particular interest to me,
> why are the gradients zero in the serial results,
> and near the GNORM in the parallel results?
> This is reflected also in the GEOMETRY.xyz files.
> (Compile time optimizations for each version differ
> a little.)
>
> Serial   3.9.1:
> *** TOTAL STEP NR.  9999           GEOMETRY STEP NR.   2284  ***
> *** GNMAX=  1.182878E-03 [5.35E-05]     ETOT=   -189.032981  ***
> *** GNORM=  2.870398E-04               DETOT=     1.005E-09  ***
> *** CNSTR=  0.000000E+00                TCPU=         80.58  ***
> ...
> =              END OF GEOMETRY OPTIMIZATION                    =
> *                        FINAL RESULTS                         *
> ...
>   ATOM          COORDINATES            GRADIENTS (-FORCES)
>   1  O  5.1224  2.8573  3.3944   0.000E+00  0.000E+00  0.000E+00
>   2  O  4.1231  8.7555 10.3710   0.000E+00  0.000E+00  0.000E+00
>   3  O 14.3880  2.7858  3.3105   0.000E+00  0.000E+00  0.000E+00
>   4  O 13.4023  8.7048 10.1629   0.000E+00  0.000E+00  0.000E+00
> ..................................................................
>
> Parallel 3.9.1:
> *** TOTAL STEP NR.  6604           GEOMETRY STEP NR.   1400  ***
> *** GNMAX=  1.825868E-03 [8.65E-09]     ETOT=   -189.032988  ***
> *** GNORM=  4.655294E-04               DETOT=    -2.749E-10  ***
> *** CNSTR=  0.000000E+00                TCPU=         18.64  ***
> ...
> =              END OF GEOMETRY OPTIMIZATION                    =
> *                        FINAL RESULTS                         *
> ...
>   ATOM          COORDINATES            GRADIENTS (-FORCES)
>   1  O  5.1271  2.8813  3.4124  -7.567E-04  9.170E-05 -4.731E-04
>   2  O  4.1229  8.6424 10.2943   6.352E-04 -9.080E-06  1.336E-04
>   3  O 14.4179  2.8784  3.3640   1.826E-03 -1.309E-04  3.528E-04
>   4  O 13.3743  8.6440 10.2220  -1.175E-03 -2.027E-04  2.011E-04
> ..................................................................
>
>
> Bob
>
>

-- 
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   Ari P Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   CNRS & IMPMC, Université Pierre et Marie Curie
       4 place Jussieu, case 115 / F-75252 Paris
   Tel: +33-1-4427 7542, Fax: +33-1-4427 3785, GSM: +33-6-6736 3820