[CP2K:2971] Re: Lowdin analysis

[Teodoro Laino]

Hi Matthias, Mahn,

The real problem is not in the basis set itself but in how the population analysis is computed in CP2K.
Diagonalizing S to evaluate S**(1/2) is probably not the smartest thing to do.

There are ways to evaluate S**(1/2), definitely numerically more stable, that would allow to have meaningful population analysis even with these "problematic" basis sets (although I still think that it's not the basis set itself to be problematic, rather the computational scheme used).

Best,
Teo

On Dec 5, 2010, at 3:06 PM, Matthias Krack wrote:

> Hi Manh,
> 
> population analyses are known to be very sensible to the basis set
> choice. I guess also in this case the TZV2P MOLOPT basis set is the
> reason for the unexpected result. The MOLOPT basis sets include
> relatively small exponents which might cause linear dependencies in
> the overlap matrix. The Lowdin population analysis requires the
> calculation of S**(1/2) which involves (in CP2K) a diagonalisation of
> the overlap matrix. However, an ill-conditioned overlap matrix will
> most likely result in a weird charge partition. Therefore, I would
> suggest to employ different basis sets, e.g. the MOLOPT-SR or the DZVP/
> TZVP basis sets.
> 
> Best,
> 
> Matthias
> 
> On 3 Dez., 17:46, Manh <manht... at gmail.com> wrote:
>> Hello everyone,
>> 
>> I calculate the Mulliken and Lowdin charges for a water molecule. The
>> results are:
>> 
>> ----------------------------------------------------------------
>> 
>>  MULLIKEN POPULATION ANALYSIS
>> 
>>  # Atom  Element  Kind  Atomic population                Net charge
>>       1     H        1           0.780838                  0.219162
>>       2     H        1           0.780981                  0.219019
>>       3     O        2           6.438182                 -0.438182
>>  # Total charge                  8.000000                  0.000000
>> 
>>  LOWDIN POPULATION ANALYSIS
>> 
>>  # Atom  Element  Kind  Atomic population                Net charge
>>       1     H        1           1.210449                 -0.210449
>>       2     H        1           1.210473                 -0.210473
>>       3     O        2           5.579079                  0.420921
>>  # Total charge                  8.000000                  0.000000
>> 
>> --------------------------------------------------------
>> 
>> I think that the Lowdin analysis has some problem.
>> 
>> Here is my input:
>> 
>> ---------------------------------------------
>> 
>> &FORCE_EVAL
>>   METHOD Quickstep
>>   &DFT
>>     BASIS_SET_FILE_NAME ../../../BASIS_MOLOPT
>>     POTENTIAL_FILE_NAME ../../../GTH_POTENTIALS
>>     RESTART_FILE_NAME H2O-RESTART.wfn.wfn
>>     &QS
>>       METHOD GPW
>>       EXTRAPOLATION ASPC
>>       EXTRAPOLATION_ORDER 3
>>     &END QS
>>     &MGRID
>>       CUTOFF 400
>>       NGRIDS 5
>>     &END
>>     &SCF
>>       MAX_SCF 20
>>       SCF_GUESS RESTART
>>       EPS_SCF 1.0E-6
>>       &OT
>>         PRECONDITIONER  FULL_SINGLE_INVERSE
>>         MINIMIZER  CG
>>       &END
>>       &OUTER_SCF
>>         MAX_SCF 10
>>         EPS_SCF 1.0E-6
>>       &END
>>       &PRINT
>>         &RESTART
>>           &EACH
>>             QS_SCF 0
>>             GEO_OPT 2
>>           &END
>>           ADD_LAST NUMERIC
>>           FILENAME RESTART.wfn
>>         &END
>>         &RESTART_HISTORY OFF
>>         &END
>>       &END
>>     &END SCF
>> 
>>     &XC
>>       &XC_FUNCTIONAL PBE
>>       &END XC_FUNCTIONAL
>>     &END XC
>> 
>>     &PRINT
>>      &MULLIKEN
>>      &END MULLIKEN
>> 
>>      &LOWDIN
>>      &END LOWDIN
>>     &END
>> 
>>   &END DFT
>>   &SUBSYS
>>     &CELL
>>    ABC [angstrom]   30 30 30
>>     &END CELL
>>     &TOPOLOGY
>>       COORD_FILE_NAME water.xyz
>>       COORDINATE xyz
>>     &END
>> 
>>     &KIND O
>>       BASIS_SET TZV2P-MOLOPT-GTH
>>       POTENTIAL GTH-PBE-q6
>>     &END KIND
>>     &KIND H
>>       BASIS_SET TZV2P-MOLOPT-GTH
>>       POTENTIAL GTH-PBE-q1
>>     &END KIND
>> 
>>   &END SUBSYS
>> 
>> &END FORCE_EVAL
>> 
>> &GLOBAL
>>   PRINT_LEVEL LOW
>>   PROJECT H2O
>>   RUN_TYPE ENERGY
>>   WALLTIME 285000
>> &END GLOBAL
>> 
>> &MOTION
>>     &GEO_OPT
>>      MAX_ITER 5000
>>      MAX_FORCE 0.00010
>>      OPTIMIZER BFGS
>>     &BFGS
>>     &END
>>   &END
>> &END
>> 
>> ------------------------------------------------
>>  the water.xyz file is
>> ----------------------------------------
>>        3
>>  water
>>   H         8.4351137971        5.1620318678       12.1510352783
>>   H         8.5534822942        3.6347695084       12.1803075532
>>   O         7.9011326518        4.3528437024       12.1874564118
>> ------------------------------------------------
>> 
>> Regards,
>> Manh
> 
> -- 
> You received this message because you are subscribed to the Google Groups "cp2k" group.
> To post to this group, send email to cp... at googlegroups.com.
> To unsubscribe from this group, send email to cp2k+uns... at googlegroups.com.
> For more options, visit this group at http://groups.google.com/group/cp2k?hl=en.
>