[CP2K:8745] Re: Isolated system Geometry Optimizations

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

Hi

sorry, the correct keyword is

CP2K_INPUT / FORCE_EVAL / SUBSYS / CELL / CELL_REF

this allows you to do constant number of grid point calculations
instead of constant cutoff. It results in smoother energy vs. volume 
curves.

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
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-----cp... at googlegroups.com wrote: -----To: cp2k <cp... at googlegroups.com>
From: Babgen Manookian 
Sent by: cp... at googlegroups.com
Date: 02/25/2017 09:39PM
Subject: [CP2K:8745] Re: Isolated system Geometry Optimizations

Hey Juerg,
So I looked in the input manual and could not find the REF_CELL keyword. Also, it is still a little unclear what is actually being changed in terms of the calculation. Could you elaborate on that for me please?
Does this have anything to do with setting density to be zero at the cell wall?
Thank you in advance,Bobby 

On Tuesday, February 14, 2017 at 1:21:43 PM UTC-5, Babgen Manookian wrote:Hey Everyone,
I am a new cp2k user and have been working on a test system in order to get a feel for how the program works. My test system is a cyclohexane molecule and I am interested in determining the energy difference between boat and chair conformations. I am using a wavelet poisson solver with periodicity turned off and the molecule centered in the cell. I attached the template input file which I used to create the different inputs with varying cells size.
What I have noticed is that as I increase my cell size the energy does not converge on a single value, instead it seems to oscillate. The graphs below show the energies of each conformation and their differences as functions of cell size. I am very curious as to what is causing these oscillations. If I have a single cyclohexane molecule centered in my cell, as I increase my cell size, I would think that the extra vacuum space around the molecule will not affect the energy. 
If there is anyone out there who could provide any sort of input on this it would be much appreciated.

Thanks,Bobby



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