[CP2K:7246] Warning when using HFX for a single molecule

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

Hi

- you can ignore the warning, even better if you explicitly switch
  off periodic images in the cell and Poisson sections.

- MOLOPT basis sets are very slow when used in HFX calculations
  (because of the very diffuse primitives). You van either
  switch to a more compact basis or use the ADMM approximation
  (see the ADMM paper by Guidon et al for more information).

regards

Juerg Hutter 
--------------------------------------------------------------
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: eft rsd 
Sent by: cp... at googlegroups.com
Date: 12/16/2015 04:34PM
Subject: [CP2K:7246] Warning when using HFX for a single molecule

Dear CP2K folk,

I have two questions about employing the &HF flag for a relatively large system.

My system consists of a single molecule made up by 70 atoms. I am using the large basis of TZV2PX-MOLOPT-GTH-qx and the PBE0 functional with vdW correction. This is how I wrote the functional flag 

######################################################
    &XC
      &XC_FUNCTIONAL
&PBE
SCALE_X 0.75
SCALE_C 1.0
&END
      &END XC_FUNCTIONAL
      &XC_GRID
            XC_DERIV SPLINE2
      &END
      &VDW_POTENTIAL
        POTENTIAL_TYPE PAIR_POTENTIAL
        &PAIR_POTENTIAL
          TYPE DFTD3
          PARAMETER_FILE_NAME ./dftd3.dat
          REFERENCE_FUNCTIONAL PBE0
          D3_SCALING 1.0 1.287 0.928 *** 22:23:54 WARNING in hfx_types:hfx_create_neighbor_cells :: Periodic   ***
 *** Hartree Fock calculation requested without use of a truncated or      ***
 *** shortrange potential. This may lead to unphysical total energies. Use ***
 *** a truncated  potential to avoid possible problems. hfx_types.F line   ***
 *** 1411                                                                  ***

        &END PAIR_POTENTIAL
      &END VDW_POTENTIAL
&HF
FRACTION 0.25
&MEMORY
MAX_MEMORY 512
EPS_STORAGE_SCALING 1.0E-1
&END MEMORY
&SCREENING
EPS_SCHWARZ 1.0E-8
&END SCREENING
&END HF
    &END XC
######################################################


The questions are:
)
1- I tested the functional on a small system of 3 atoms and that was done within hours. However, for the large system of 70 atoms the calculations took ages (and were finally interrupted due to resource limits). The questions is: Is this a normal calculation period for HF? Are there CP2K options that I can use to speed up the calculations?

2- When I checked what was printed out in the log file I found the following message:

 *** 22:23:54 WARNING in hfx_types:hfx_create_neighbor_cells :: Periodic   ***
 *** Hartree Fock calculation requested without use of a truncated or      ***
 *** shortrange potential. This may lead to unphysical total energies. Use ***
 *** a truncated  potential to avoid possible problems. hfx_types.F line   ***
 *** 1411                                                                  ***

Since this is a single molecule (in a very large box), can I safely ignore the warning?


Thanks,
ER




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