cp2k - ab initio simulations - reproduction of the denisty for condensed phases

[Anna Wójcik]

W dniu poniedziałek, 14 marca 2016 15:09:32 UTC+1 użytkownik Anna Wójcik 
napisał:
>
> Hi :)
> I'm a new user of cp2k program. Till now I was using only QM, QM/MM and 
> sometimes MD methods (MD only to model enzyme structure before QM or 
> QM/MM), but I need to use cp2k for requirement parametrization of some 
> molecules. I did some test modelling on condensed phase including 30 
> molecules of triacetin and also for 30 water molecules as a reference, but 
> so far I'm receiving overestimated density for triacetin and for water. 
> Ab-initio MD was lasting about 2 ps using NPT ensemble. The model was 
> equilibrated using classical MD in GROMACS in OPLS force field, afterwards 
> I chose two geometries which have density equal to experimental one and box 
> size I took exactly for these geometries from classical MD, than I did 3000 
> steps in NVT ensemble of ab initio MD using cp2k and because temperature 
> was OK, and all energies including ConsQty reached plateau I performed 
> ab-initio MD in NPT ensemble, but in all models I reached overestimated 
> density and the error equals about 0.1 g/cm3 in all models tested for 
> triacetin and for water. My question is: Do You have any suggestion what is 
> the reason?? Maybe the reason is an algorithm or maybe settings or maybe 
> simulations were to short or models two small?? Or maybe for calculations 
> in NPT ensemble I should took bigger box than in classical MD?
> I would be very grateful for any suggestions
>

Anna Wójcik, Krakow, Poland, Jagiellonian University 
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