From NWChem
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2:17:28 AM PDT  Tue, Jul 23rd 2013 

Hello all,
I would like to extend a work involving the PBE0 functional started with MOLPRO and to continue it with NWCHEM. However, it seems that the energies provided by the default PBE0 methods are not the same for a calculation of the ground state of the carbon atom.
Here are the parameters of the DFT functional in MOLPRO:
Density functional group PBE0=PBEX+PBEC
Functional: PBEX(Automatically generated (new) PBEX) Gradient terms: 1
Functional: PBEC(Automatically generated (new) PBEC) Gradient terms: 1
Exact exchange will be calculated, factor: 0.2500
Functional: PBEX Factor: 0.7500
Functional: PBEC Factor: 1.0000
and the same in NWCHEM:
PBE0 Method XC Functional
HartreeFock (Exact) Exchange 0.250
PerdewBurkeErnzerhof Exchange Functional 0.750
Perdew 1991 LDA Correlation Functional 1.000 local
PerdewBurkeErnz. Correlation Functional 1.000 nonlocal
What are the differences between the two software packages' default implementation of PBE0, i.e. can their PBE0 definitions/implementations be adjusted?
I tried the default B3LYP functional as well and I have the same problem.
My nwchem input for carbon atom is:
geometry
zmatrix
C;
end
end
basis
C library 631g
end
scf
thresh 1.0e5
end
task scf
dft
xc pbe0
convergence energy 1.0e6
convergence gradient 1.0e6
end
task dft
Thanks in advance,
Sincerely yours,
Guillaume




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9:18:49 AM PDT  Tue, Jul 23rd 2013 

Guillaume
could you please try an atom where all shells are completely filled, e.g. a gas such as
helium or neon?
If you need to compute DFT atomic energies, the situation requires to somewhat enforce spherical symmetry
and there a few different ways to do it ... and it is possible that Molpro is doing that.
In the case of atoms with completely filled shells there is not any ambiguity of the sort mentioned above.
Cheers, Edo




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1:38:13 AM PDT  Wed, Jul 24th 2013 

Deers Edo
I have already done a calculation of the ground state of a neon atom and I have the same problem.
Moreover, I compute using a cartesian basis set for HF method in MOLPRO and NWCHEM. For the HF method, the value of energies are exactly the same (in the case of carbon and neon atom).
I am going to take a look at the spherical symmetry in MOLPRO.
Thanks,
Guillaume




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9:24:23 AM PDT  Wed, Jul 24th 2013 

Guillaume
If the Ne energy disagrees, we can exclude the atomic symmetry as a factor.
A possible source of discrepancy is the LDA component used by the Correlation PBE functionals.
NWChem makes use of the PerdewWang 1991 functional for the LDA bit of PBE Correlation,
can you tell what is Molpro using?
Edo




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10:52:25 AM PDT  Wed, Jul 24th 2013 

Agreement to 5 digits

Guillaume,
I have tried the calculation myself on both codes and I am getting a 5 digits agreement on the total energy of
128.78985 hartrees
NWChem output file (input echeod at the top)
http://www.nwchemsw.org/images/Ne.nwout
Molpro input file
http://www.nwchemsw.org/images/Ne_molproinput.nw




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12:53:54 PM PDT  Mon, Aug 19th 2013 

Which version of MOLPRO are you using? MOLPRO 2009 and older versions define a different PBE0 functional.
http://www.molpro.net/pipermail/molprouser/2009December/003459.html



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