[CP2K:7532] cp2k - ab initio simulations - reproduction of the denisty for condensed phases

[hut... at chem.uzh.ch]

Hi

two possible sources for your results:

1) convergence of density. NPT is often difficult to equilibrate
   and can depend on the choice of parameters for the barostat

2) choice of DFT functional, especially the treatment of vdW energy.
   Have a look into the recent extensive literature on the density of
   water using different approaches. Changes of 0.1 g/ml are very
   common.

regards

Juerg 
--------------------------------------------------------------
Juerg Hutter                         Phone : ++41 44 635 4491
Institut für Chemie C                FAX   : ++41 44 635 6838
Universität Zürich                   E-mail: hut... at chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

-----cp... at googlegroups.com wrote: -----To: cp2k <cp... at googlegroups.com>
From: Anna Wójcik 
Sent by: cp... at googlegroups.com
Date: 03/14/2016 03:09PM
Subject: [CP2K:7532] cp2k - ab initio simulations - reproduction of the denisty for condensed phases

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



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