Partial charges on the atom
Clicked A Few Times
8:37:09 AM PDT - Mon, Apr 27th 2015
Hi all,

Is it possible to have a partial charge when doing a QM energy calculation in nwchem? or is that even possible in Quantum physic calculation?

Thank you!

Forum Regular
12:48:19 PM PDT - Mon, Apr 27th 2015
Within the geometry block, you can specify an arbitrary nuclear charge for each atom. The charge directive is then used to set the number of electrons in the system with the constraint that the number of electrons must be an integer. So it is possible for the total charge of the systems to be non-integer, but the number of electrons must always be an integer.
For example:

geometry
H  0.0  0.0 -0.5 charge 1.25

H  0.0  0.0  0.5 charge 1.25
end
charge 0.5

would simulate H2 with 2 electrons and a total charge of 0.5

Best,
Sean

Clicked A Few Times
3:50:16 AM PDT - Fri, May 1st 2015
Thank you, however I have an error after submitting this input file:

start MgMOF-74
title "MgMOF-74"

memory 5000 mb
geometry
C 8.59886355 17.68912997 15.23024421
O 7.79422064 18.43388815 14.85345853
O 9.40505759 16.94410501 15.60704709
Mg 7.88418289 20.67609980 14.51097681 charge 13.5
end
basis
 C library 6-31+G*

 O library 6-31+G*

 Mg library 6-31+G*
end
charge 1.5

scf
uhf
singlet
end

It gives me this error: 



     Superposition of Atomic Density Guess

     -------------------------------------
      • The number of electrons -1 in the ECP does not
accord with a known set of completely filled shells !!!
------------------------------------------------------------------------

unrecognised pseudopotential      911

------------------------------------------------------------------------

There is an error in the input file

------------------------------------------------------------------------

For more information see the NWChem manual at 

http://nwchemgit.github.io/index.php/NWChem_Documentation




For further details see manual section: 

                                                                               

                                                                               

Can you help me with that because I do not know what is wrong. Thank you!

Forum Regular
3:10:33 PM PDT - Fri, May 1st 2015
The error is being caused by the assigned nuclear charge not playing nice with the set up for the atomic scf guess. The easiest fix is to switch your initial guess to hcore, i.e.

scf
uhf
singlet
vectors input hcore
end

This should eliminate the error and my test calculation ran successfully.

Best,
Sean

Clicked A Few Times
3:47:49 AM PDT - Tue, May 12th 2015
Thanks it is working now!

Clicked A Few Times
3:48:03 AM PDT - Tue, May 12th 2015
Thanks it is working now!

Clicked A Few Times
3:48:05 AM PDT - Tue, May 12th 2015
Thanks it is working now!

Clicked A Few Times
3:48:07 AM PDT - Tue, May 12th 2015
Thanks it is working now!

Clicked A Few Times
9:39:33 AM PDT - Mon, May 18th 2015
Hi sorry to bother again. Can you tell me if it is possible to have 33 electrons, 34 proton but + 1.5 charge in total? If it is possible, how can I do it?

Thank you.

Forum Regular
10:52:18 AM PDT - Mon, May 18th 2015
If you would like a system with 33 electrons and a total nuclear charge of +34 while having a total charge of +1.5, you would have to add an external point charge (see http://nwchemgit.github.io/index.php/Release65:Bq)
For example:

geometry
C 8.59886355 17.68912997 15.23024421
O 7.79422064 18.43388815 14.85345853
O 9.40505759 16.94410501 15.60704709
Mg 7.88418289 20.67609980 14.51097681
end
basis print
C library 6-31+G*
O library 6-31+G*
Mg library 6-31+G*
end

charge 1.0

bq
0.0000 0.0000 0.0000 0.5
end

scf
uhf
doublet
vectors input hcore
end
task scf

The charge directive only considers the nuclear charge, hence the charge of +1 in order to get 33 electrons and then the Bq charge of +0.5 so that the total charge of the system should be +1.5.


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