[CP2K:9590] SCF_GUESS

[Xiaoming Wang]

Dear Prof. Hutter,

I encountered the same problem again. I am doing simple ENERGY 
calculations. I have reduced the EPS_SCF to 1.0E-8, but still the total 
energy I obtained are different for the two cases: one is using SCF_GUESS 
of ATOMIC, and the other is RESTART, where the restart wave function is 
from a converged one of a similar structure with several atoms slightly 
distorted.  Other features of my calculation are ROKS and SIC included.  I 
am wondering why those two setups give such different results. The energy 
difference can be as large as 0.01 Ha. Following is my input:

&GLOBAL

  PROJECT_NAME SS

  RUN_TYPE ENERGY

  PRINT_LEVEL MEDIUM

&END GLOBAL

&FORCE_EVAL

  METHOD QS

  &DFT

    BASIS_SET_FILE_NAME BASIS_MOLOPT

    POTENTIAL_FILE_NAME GTH_POTENTIALS

    WFN_RESTART_FILE_NAME SS-RESTART.wfn

    MULTIPLICITY 3

    ROKS

    &SIC

     SIC_METHOD EXPLICIT_ORBITALS

     SIC_SCALING_A 0.30

     SIC_SCALING_B 0.00

    &END SIC

    &MGRID

      CUTOFF 400

      REL_CUTOFF 40

    &END MGRID

    &XC

      &XC_FUNCTIONAL PBE 

      &END XC_FUNCTIONAL

    &END XC

    &SCF

      MAX_SCF 20

      EPS_SCF 1.0e-8

      CHOLESKY INVERSE

      SCF_GUESS RESTART

      &OT

       ROTATION

       PRECONDITIONER FULL_KINETIC

       ENERGY_GAP 0.01

       LINESEARCH 3PNT

      &END OT

      &OUTER_SCF

       EPS_SCF 1.0e-8

       MAX_SCF 50

      &END OUTER_SCF

    &END SCF
  &END DFT 
  &SUBSYS
   ....
   &END SUBSYS

&END FORCE_EVAL



Best,
Xiaoming


On Friday, October 27, 2017 at 4:32:51 AM UTC-4, jgh wrote:
>
> Hi 
>
> SCF_GUESS (RESTART/ATOMIC) is just for the very first guess, 
> meaning the first SCF iteration in the first step of a MD. 
>
> For initial guesses within one calculation (one MD step to the 
> next) you have to use 
>
> FORCE_EVAL / DFT / QS / EXTRAPOLATION  xxxxx 
>
> In any case, if the final result depends on any of these 
> choices, you have another problem, e.g. your convergence criteria 
> is not strict enough, or one calculation did not converge within the 
> given number of steps etc. 
>
> 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 
> <javascript:> 
> Winterthurerstrasse 190 
> CH-8057 Zürich, Switzerland 
> --------------------------------------------------------------- 
>
> -----cp... at googlegroups.com <javascript:> wrote: -----To: cp2k <
> cp... at googlegroups.com <javascript:>> 
> From: Xiaoming Wang 
> Sent by: cp... at googlegroups.com <javascript:> 
> Date: 10/26/2017 05:28AM 
> Subject: [CP2K:9590] SCF_GUESS 
>
> Dear all, 
> For BAND, OPT or MD calculations, one usually sets SCF_GUESS to RESTART, 
> which will use the WFN of the previous step as a initial guess. This will 
> usually accelerate the convergence of the SCF loops. However, The result is 
> different from that with SCF_GUESS sed to ATOMIC. I am confused why the 
> final results depend on the initial guess of the wfn. 
> Best,Xiaoming 
>
>
>
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