[DFTB-Plus-User] keeping charges on selected atoms constant

Jakub Kaminski kaminski at caltech.edu
Tue Oct 30 17:46:19 CET 2012


Dear Ben,

I'm trying to look at the changes of density upon oxidation in a cluster of molecules. Using waveplot I'm plotting density difference maps between oxidized and ground-state cluster. I have noticed that the molecules laying on the outside of my cluster (i.e. the ones  in contact with vacuum) experience the most perturbation in density upon oxidation, while the ones buried inside - much less. There might be some explanation of this effect coming from theory, or the flaws in approximations, using cluster model, etc... (haven't got time to really look at it yet). In the meanwhile, I wanted to try to "force" oxidation in the inside of my cluster by fixing the charge of the outside molecules. 

Best,
Jakub


On Oct 30, 2012, at 3:37 AM, Ben Hourahine wrote:

> Dear Jakub,
> 
> could you explain what are you trying to simulate? As Bálint mentioned, there are several
> ways to make this type of constraint, but these are not in the standard code, in part as
> it requires some care to make sure the results of such constraints are meaningful.
> 
> Regards
> 
> Ben
> 
> On 29/10/12 23:24, Jakub Kaminski wrote:
>> Dear all,
>> 
>> is there a possibility in DFTB+ to perform calculations where I assign initial charges to some atoms and keep them frozen during SCC iterations, while optimizing remaining charges in the system? Maybe I overlooked, but I don't see such an option in manual.
>> 
>> Best regards,
>> Jakub Kaminski
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> 
> -- 
>     Dr. B. Hourahine, SUPA, Department of Physics,
>   University of Strathclyde, John Anderson Building,
>          107 Rottenrow, Glasgow G4 0NG, UK.
>    +44 141 548 2325, benjamin.hourahine at strath.ac.uk
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