[CPMD-list] forces, convergence and gga

[De Dobbelaere Christopher]

Hi cpmd users,

I've got 3 little questions..

1) I'm doing a md run of a molecule surrounded by water molecules. In order to check if the forces acting on the molecules are not too large, i'd like to check out the forces acting on them (since i didn't do a geometry optimalization at the beginning). I checked out the manual and found that it is possible to print the acting forces during the trajectory in the TRAJECTORY file. Since the md run is 'finished' it seems to be a little late for that..
But now I was wondering what the initial forces acting on the atoms would be. Since they are listed in the output file that seemed not to be a problem. But what are the units of the forces? They are not mentioned in the manual, so i suppose it's a.u.? If it it, what's the conversion to convert them to dyne, Newton,.. or something else?

2) Before I did a md run, i checked out some dft functionals to describe the geometry of the molecule. I got convergence for C=C, C-H, more or less convergence for S-N but the C-S bound  seems not to convergence at all (the C's from a aromatic system and C is attached to it). Does anyone have an idea why that could be? 

3) In the manual, the GGA functional is mentioned. But what's the exact functional behind that GGA implemented in cpmd? Since GGA stands for Generalized-gradient-approximation, it doesnt give me any new information..

Thanks in advance!

 

Christopher
Undergrad. Student
University of Antwerp

 
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