[CPMD-list] combination of PBE USPP with BLYP DFT

[Axel Kohlmeyer]

>>> "ES" == Erik Emilio Santiso <eesantis at unity.ncsu.edu> writes:

ES> Hi! Well, this looks more like a coincidence than anything else. I don't
ES> think it makes any sense to find a PP with one xc functional and then do
ES> the calculation with another one.

yep. please have a look the documentation that comes along with 
the vanderbilt pseudopotential generation software. it says,
you first run an all-electron calculation for the reference
configuration where you have to specify the exchange-correlation type
and then generate a pseudopotential from the results of that
calculation.

the best first order approximation you probably could do, is to
generate the pseudopotential with the same parameters, but for BLYP
(look for the parameter 'exfact' in the all electron input file) instead
of PBE, and repeat your calculations with these potentials. but before
using them for anything serious, you should _carefully_ test those 'new' 
pseudopotentials on some simple and representative examples.

hope this helps,
     axel.


ES> Erik.

ES> On Thu, 30 Oct 2003, Jung Goo Lee wrote:

>> Hi everyone,
>> 
>> I would like to know whether the combination of PBE uspp in ATOMS option
>> and BLYP in DFT
>> option (the example of partial input is shown below)makes sense or not,
>> especially, for calculations
>> of free energy (constraint). This is because BLYP method underestimate
>> the dissociation free energy
>> compared with experiment. For example,  water dissociation in 32 water
>> molecules with MT PP/
>> BLYP method gave 17 kcal/mol in free energy while experimental value is
>> 21 kcal/mol(Trout and
>> Parrinello, Chem. Phys. Lett, 288(1998)343.
>> I tried the same calculation with PBE uspp and BLYP method.
>> I got about 20 kcal/mol althogh I tried with  a few hundred fs (instead
>> of 1 ps) MD at each point of
>> O-H bond constraint. So, this combination (PBE uspp/BLYP) seems to be
>> o.k. in free energy
>> calculations.
>> 
>> Is this a reasonable and cheap(computationally) way to get out of the
>> problem with free energy
>> calculations with gbl uspp/BLYP?
>> Does any one have any rationalization or contradiction with reasonable
>> explanation?
>> 
>> Jung-Goo Lee
>> 
>> Example
>> --
>> --
>> &ATOMS
>> *008-O-gpbe--bm.uspp NEWF BINARY
>> LMAX=P
>> 1
>> 4.3728  4.5000  4.5000       1   8
>> 
>> *001-H-gpbe--bm.uspp NEWF BINARY
>> LMAX=S
>> 2
>> 5.5172  4.5000  5.9238       1   1
>> 5.5172  4.5000  3.0761       1   1
>> &END
>> 
>> &DFT
>> OLDCODE
>> FUNCTIONAL BLYP
>> GRADIENT CORRECTION BECKE88 LYP
>> LDA CORRELATION LYP
>> &END
>> --
>> --
>> 
>> 
>> _______________________________________________
>> CPMD-list mailing list
>> CPMD-list at cpmd.org
>> http://www.cpmd.org/mailman/listinfo/cpmd-list
>> 
ES> _______________________________________________
ES> CPMD-list mailing list
ES> CPMD-list at cpmd.org
ES> http://www.cpmd.org/mailman/listinfo/cpmd-list



--
=======================================================================
Axel Kohlmeyer       e-mail: axel.kohlmeyer at theochem.ruhr-uni-bochum.de
Lehrstuhl fuer Theoretische Chemie          Phone: ++49 (0)234/32-26673
Ruhr-Universitaet Bochum - NC 03/53         Fax:   ++49 (0)234/32-14045
D-44780 Bochum  http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.