[CP2K-user] [CP2K:16207] Unexpected finite size effects water AIMD

[James Suttig]

Dear All

I require the average potential energy per water molecule for 
thermochemical calculations. However, I find that the average PE differs 
significantly (by ~1-8 kJ/mol) for different system sizes. Based on 
classical simulations, this is quite unexpected. There is the possibility 
that the simulations have not equilibrated yet, but the PEs seem to have 
reasonably plateaued (see attached figure). The length of the trajectories 
are also already similar to those reported in (older) papers.   

The DFT settings used for each system are the same, and are summarized by 
the input lines appended to the end of this email. In all cases the 
temperature set to 330 K. For reference, I've also attached restart files 
for each system. 

Any insight as to why these finite size effects are observed would me much 
appreciated. Could there be a "DFT reason" that I am not aware of?

Best Regards,
James
________________________________________

     &MGRID
       CUTOFF     3.2000000000000000E+02
       REL_CUTOFF     4.0000000000000000E+01
     &END MGRID
     &XC
       DENSITY_CUTOFF     1.0000000000000000E-10
       GRADIENT_CUTOFF     1.0000000000000000E-10
       TAU_CUTOFF     1.0000000000000000E-10
       &XC_GRID
         XC_SMOOTH_RHO  NN10
         XC_DERIV  SPLINE2_SMOOTH
       &END XC_GRID
       &XC_FUNCTIONAL  NO_SHORTCUT
         &PBE  T
         &END PBE
       &END XC_FUNCTIONAL
       &VDW_POTENTIAL
         POTENTIAL_TYPE  PAIR_POTENTIAL
         &PAIR_POTENTIAL
           R_CUTOFF     1.6000000000000000E+01
           TYPE  DFTD3(BJ)
           PARAMETER_FILE_NAME ../input/dftd3.dat
           REFERENCE_FUNCTIONAL PBE
         &END PAIR_POTENTIAL
       &END VDW_POTENTIAL



-- 
You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp2k+unsubscribe at googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cp2k/1f3b60dd-d06f-4b10-810d-1bc9cde4d9e1n%40googlegroups.com.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20211110/f426e458/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: plotPEall.png
Type: image/png
Size: 74341 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20211110/f426e458/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: restart-water-N80.inp
Type: chemical/x-gamess-input
Size: 45408 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20211110/f426e458/attachment.inp>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: restart-water-N120.inp
Type: chemical/x-gamess-input
Size: 65459 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20211110/f426e458/attachment-0001.inp>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: restart-water-N348.inp
Type: chemical/x-gamess-input
Size: 179688 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20211110/f426e458/attachment-0002.inp>