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Counterpoise in MOLCAS (Read 2752 times)
Gerrit-Jan Linker
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Counterpoise in MOLCAS
01.12.10 at 17:36:17
Counterpoise in MOLCAS
To perform the Counterpoise procedure in MOLCAS the charge parameter can be used in the basisset definition in the SEWARD input to make dummy or ghost atoms. These are placeholders for basisfunctions only. They are input as normal atoms but with the charge of the atoms set to 0. They will therefore not generate a field due to the nuclear charge.
The Counterpoise procedure is used to calculate the bonding energy of a system AB. When calculating the AB system and the A and B system separately the bonding energy cannot be calculated simply as  
Ebonding = EAB - (EA+EB)
The reason is that in the AB system, fragment A is described in the complete basis of A and B. The same applies for B. In AB the basisset is larger for the subsystems than in the isolated systems A and B. This is the so called basisset superposition error (BSSE) for which we need to correct.
The procedure is to calculate fragment A in the complete basis of AB and to do the same for fragment B. The thus obtained energies for A and B can then be used in the above formula to compute the bonding energy. AB, A and B are all 3 calculated in the same basis.
To perform this procedure is to set the charge to 0 in the basisset definition in SEWARD. Example:
Basis  set  
Ni.Uncontracted...4s4p4d.  /  AUXLIB  
Nix  0.00000  0.00000  0.000000  Bohr  
End  of  basis  
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« Last Edit: 01.12.10 at 17:42:45 by Gerrit-Jan Linker »  

Gerrit-Jan Linker
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