[CP2K:3477] energy convergence question

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

Hi

if you change the box size for a given cutoff you might get
oscillations due to the integer number of grid points.

- Test the cutoff for a fixed box size by increasing the cutoff
  (I would use larger intervals and higher cutoffs if convergence
    is important)

- find the best box size at this cutoff by enlarging the box.
  Use isolated boundary conditions (Ewald method and periodicity none)
  for best results.

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
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-----cp... at googlegroups.com wrote: -----
To: cp... at googlegroups.com, s.me... at caspur.it
From: Alin Marin Elena 
Sent by: cp... at googlegroups.com
Date: 08/31/2011 01:06PM
Subject: [CP2K:3477] energy convergence question

Dear All,


I try to determine the good box size and density cut-off for a small cluster 
(HF(H_2O)_7) for HCTH120 functional.
However the results that I obtained left me with few questions.
I played with three functionals PBE, BLYP and HCTH120 for different cut-offs 
(280 to 330 in step of 10Ry and Ngrid 5) and plotted the total energy for each 
of them against the box size (a cube) -- see the attached figures pbe.eps, 
blyp.eps and hcth.eps. The calculation seems to converge after but I am a 
little bit troubled by the oscillation that shows. 

Do I miss anything in my input that gives this behaviour?
I attached the input files too..

I used the TZV2P basis set from this
# Joost VandeVondele and Juerg Hutter
# J. Chem. Phys. 127, 114105 (2007)
# URL: http://link.aip.org/link/?JCP/127/114105
# DOI: 10.1063/1.2770708

and the GTH potentials.

I also investigated two other basis sets TZVP and TZV2PX the behaviour is the 
same.. just the energies different as expected...

Alin




-- 
 Without Questions there are no Answers!
 _____________________________________________________________________
  Alin Marin ELENA
  Advanced Molecular Simulation Research Laboratory
  School of Physics, University College Dublin
  ----
  Ardionsamblú Móilíneach Saotharlann Taighde
  Scoil na Fisice, An Coláiste Ollscoile, Baile Átha Cliath

  -----------------------------------------------------------------------------------
  http://alin.elenaworld.net
  ______________________________________________________________________


[attachment "blyp.eps" removed by Jürg Hutter/at/UZH]
[attachment "hcth120.eps" removed by Jürg Hutter/at/UZH]
[attachment "pbe.eps" removed by Jürg Hutter/at/UZH]
[attachment "inputs.tar" removed by Jürg Hutter/at/UZH]
[attachment "signature.asc" removed by Jürg Hutter/at/UZH]