From NWChem
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Just Got Here
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| 10:02:58 AM PST - Tue, Nov 20th 2012 |
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Dear all,
I'm a NWChem newbie and I'm performing single point calculations on a water geometry with both NWChem and Gaussian. I'm working at the DFT level, using the BP86 exchange-correlation functional and the 6-311G* basis set. It may seem really trivial, but I can't get comparable energies (i.e. equal to the 7-8th digit) from the two programs. I also tried following the suggestions posted here: http://comp.chem.umn.edu/info/NWChem.html with little change. Here are my input files:
NWChem
title "w sp"
geometry
O 0.00000 0.00000 0.00000
H 0.92264 0.65241 0.00000
H -0.92264 0.65241 0.00000
end
charge 0
scf
singlet
rhf
end
dft
xc slater 1.0 becke88 nonlocal 1.0 perdew86 1.0 vwn_1_rpa 1.0
iterations 5000
grid lebedev 90 14 ssf euler
end
basis "ao basis" spherical
o library 6-311g*
h library 6-311g*
end
task dft
ecce_print w_dft
Gaussian
%nproc=4
# bp86/6-311g* scf=(tight) nosym integral(grid=ultrafine)
w sp
0 1
O 0.00000 0.00000 0.00000
H 0.92264 0.65241 0.00000
H -0.92264 0.65241 0.00000
The energies I get are:
NWChem : -76.600926730992
Gaussian: -76.4024349388
which are indeed very different. The same happens if I change the functional to B3LYP, even if the difference is much less dramatic.
I am probably doing something wrong but I don't understand what. Do you have any suggestions?
Thank you
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Edited On 10:06:23 AM PST - Tue, Nov 20th 2012 by Clef
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Edoapra Forum:Admin, Forum:Mod, bureaucrat, sysop
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Forum Vet
Threads 8
Posts 1374
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| 10:13:19 AM PST - Tue, Nov 20th 2012 |
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use xc becke88 perdew86
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If you use xc becke88 perdew86, the energy computed by NWChem is -76.402352654964
dft
# xc slater 1.0 becke88 nonlocal 1.0 perdew86 1.0 vwn_1_rpa 1.0
xc becke88 perdew86
iterations 5000
grid lebedev 90 14 ssf euler
end
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Just Got Here
Threads 2
Posts 4
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| 2:45:16 PM PST - Tue, Nov 20th 2012 |
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Thank you! I had used that explicit expression for BP86 because of an e-mail I had found (here). Is that wrong?
Another thing, I see that nwchem supports the resolution of identity approximation for MP2, but I'm not sure about dft... is it possible?
Thank you again
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Edoapra Forum:Admin, Forum:Mod, bureaucrat, sysop
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Forum Vet
Threads 8
Posts 1374
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| 2:57:22 PM PST - Tue, Nov 20th 2012 |
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Clef,
I am not commenting on definitions that don't see to work ...
The DFT equivalent of RI-MP2 requires the definition of a second basis set, i.e. charge density fitting basis set
More details at
http://www.nwchem-sw.org/index.php/Release61:Density_Functional_Theory_for_Molecules#Speci...
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Just Got Here
Threads 2
Posts 4
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| 11:18:07 PM PST - Tue, Nov 20th 2012 |
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I see; so to use the ri approximation I simply have to define the auxiliary basis set. Very nice! I will try it as soon as possible
Thank you again
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