Warning when using HFX for a single molecule

eft rsd rashe... at gmail.com
Wed Dec 16 16:35:27 CET 2015


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                        
                              
        &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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