[CP2K:420] Re: grid settings

[Juerg Hutter]

Hi

this is a GAPW calculation. The charge you refer to is only
the charge on the equidistant PW grid. The total charge
on all grids is for your input

Total Rho_soft + Rho1_hard - Rho1_soft (r-space):               -1.9999999929

As Teo already pointed out you can improve the energy by
using another Poisson solver and/or increasing the box size.
If you also use a higher cutoff for the grid, e.g.

     &MGRID
         CUTOFF  360
     &END

You get to an energy of

-1.15977265992678

that is only 1.4*10^-6 Hartree different from GAMESS.

GAPW uses a one center expansion of the density based on
the basis set used. For small basis sets (like 6-31G*)
this leads to rather small expansions and some errors
are introduced. It's expected that this error is reduced
for larger (with more primitives) basis sets.

regards

Juerg Hutter

----------------------------------------------------------
Juerg Hutter                   Phone : ++41 44 635 4491
Physical Chemistry Institute   FAX   : ++41 44 635 6838
University of Zurich           E-mail: hut... at pci.uzh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland
----------------------------------------------------------


On Thu, 29 Nov 2007, nicol... at gmail.com wrote:

>
> I forgot to mention the results I get:
>
> Total energy:
> gamess = -1.1597712381
> cp2k = -1.1598787278
>
> total electron number:
> gamess = 1.9999986580
> cp2k = -1.9869016182
>
> On Nov 29, 8:40 pm, "nicol... at gmail.com" <nicol... at gmail.com>
> wrote:
>> Hello list,
>>
>> I am trying to get familiar with cp2k and wrote a very simple H_2 DFT
>> input file. I compare the result with gamess. I somehow can't seem to
>> get both into very good agreement. I suspect that this is a grid issue
>> within cp2k since the total electron charge is not very close to 2.
>> Could someone on this list give me a hint as to what I need to change
>> in the input file to get better answers?
>>
>> Thanks already,
>>
>> nick
>>
>> gamess input file:
>>
>>  $CONTRL
>>    EXETYP=RUN
>>    DFTTYP=BLYP
>>    RUNTYP=GRADIENT
>>    COORD=UNIQUE
>>    UNITS=ANGS
>>  $END
>>  $SYSTEM TIMLIM=1 MEMDDI=1 PARALL=.TRUE. $END
>>  $BASIS GBASIS=N31 NGAUSS=6 $END
>>  $GUESS GUESS=HUCKEL $END
>>  $DATA
>> Hydrogen molecule
>> Cnv      1
>>
>> HYDROGEN   1.0   0.0   0.0   0.85
>> HYDROGEN   1.0   0.0   0.0   0.0
>>  $END
>>
>> cp2k input file
>>
>> &FORCE_EVAL
>>   METHOD Quickstep
>>   &DFT
>>     &SCF
>>       SCF_GUESS ATOMIC
>>     &END SCF
>>     &XC
>>       &XC_FUNCTIONAL BLYP
>>       &END XC_FUNCTIONAL
>>     &END XC
>>     &QS
>>       METHOD GAPW
>>     &END QS
>>     &POISSON
>>       POISSON_SOLVER ANALYTIC
>>       PERIODIC NONE
>>     &END POISSON
>>   &END DFT
>>   &SUBSYS
>>     &CELL
>>       ABC 7.0 7.0 7.0
>>       PERIODIC NONE
>>       UNITS ANGSTROM
>>     &END CELL
>>     &COORD
>>       H 0.0 0.0 0.85
>>       H 0.0 0.0 0.0
>>     &END COORD
>>     &KIND H
>>       BASIS_SET 6-31G*
>>       POTENTIAL ALL
>>     &END KIND
>>   &END SUBSYS
>> &END FORCE_EVAL
>> &GLOBAL
>>   PROJECT H2-cp2k
>>   RUN_TYPE ENERGY_FORCE
>> &END GLOBAL
> >
>