[CP2K:4029] Re: Energy conservation NVT/NVE simulation

[hut... at pci.uzh.ch]

Hi

I did some tests with the inputs from
../tests/Fist
and get much better energy conservation that you show.
Probably your input use a not optimal setting for the
cutoffs and Ewald parameters (I was using SPME).

regards

Juerg 

--------------------------------------------------------------
Juerg Hutter                         Phone : ++41 44 635 4491
Physical Chemistry Institute   FAX   : ++41 44 635 6838
University of Zurich               E-mail:  hut... at pci.uzh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland
---------------------------------------------------------------

-----cp... at googlegroups.com wrote: -----
To: cp... at googlegroups.com
From: marco masia 
Sent by: cp... at googlegroups.com
Date: 09/12/2012 03:39PM
Subject: [CP2K:4029] Re: Energy conservation NVT/NVE simulation

Dear all,

recently I have noticed the same problem with FIST simulations. I took the H2O-32_ewald.inp input, equilibrated it for 1 ns and run a 1ns NVE simulation from the thermalized configuration. I have tried to refine many simulation parameters (e.g. time step, RCUT, Ewald pars) and also (thinking that there was a bad implementation of constraints) I run the simulations for a flexible model. I always get a non-negligible drift (see attachment); the graph shows block averaged energies of 1 ns simulations performed with cp2k and obeli.x (a program of mine). The values are shifted for a better comparison. I have been looking into this, thinking that the problem was in the input file...but since other people are experiencing it with QS, I wonder if there is some bug in the velocity verlet routines. The results are platform independent (I tried both on mac and linux).

best

marco

On Wednesday, September 5, 2012 3:32:26 AM UTC-4, albe... at virgilio.it wrote:
Dear all,

I'm carrying out some tests to reproduce the VDOS of water and I used as
starting points the input files 'H2O-32.inp' and 'H2O-64.inp' in
tests/QS/benchmark directory.

In both cases I ran a NVT simulation at 300K for 15 ps followed by an NVE
simulation on the equilibrated system.

I'm puzzled about the results in the energies: in both NVT and NVE  the plot of
"Cons Qty" show a constant and linear drift while temperature, kinetic and
potential energy are equilibrated and stable.

Since "Cons Qty" should be conserved and this is not the case I think that
there are some problems in the setup of the simulation.
I did not modify the parameters of the benchmark inputs but I just added the
thermostat section in NVT and I modified only the printing option.

Thank you very much for your help and suggestions,

Alberto

  
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[attachment "energy-conservation.pdf" removed by Jürg Hutter/at/UZH]