SCF_GUESS

[Xiaoming Wang]

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 an initial guess. This will usually accelerate the convergence of the SCF loops. However, The result is different from that with SCF_GUESS set to ATOMIC. I am confused why the final results depend on the initial guess of the wfn.

Best,

Xiaoming

[hut...@chem.uzh.ch]

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...@chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

-----cp...@googlegroups.com wrote: -----To: cp2k <cp...@googlegroups.com>
From: Xiaoming Wang
Sent by: cp...@googlegroups.com
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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[Xiaoming Wang]

Thanks!

[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:

[Matt W]

Assuming that the calculation converged, they might converge to different electronic states.

You could try and look at Mulliken spin densities or some other indicator to see if the solutions seem different.

Matt

[Xiaoming Wang]

Hi Matt,

You're right. After looking at the spin components, the two calculations did converge to quite different solutions. So which one should I trust? The one with lowest energy? But if I set  SCF_GUESS as ATOMIC, I cannot manage to find the that solution with RESTART. How could that be?

Best,

Xiaoming

[hut...@chem.uzh.ch]

Hi

I don't have experience with the application of ROKS+SIC methods.
As Matt already mentioned, it is well possible that there are
multiple minima and the best you can do is to follow a chosen
solution. Monitoring that you don't have transitions between
solutions during MD.

regards

Juerg

--------------------------------------------------------------
Juerg Hutter Phone : ++41 44 635 4491
Institut für Chemie C FAX : ++41 44 635 6838
Universität Zürich E-mail: hut...@chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

-----cp...@googlegroups.com wrote: -----To: cp2k <cp...@googlegroups.com>
From: Xiaoming Wang
Sent by: cp...@googlegroups.com

Date: 01/26/2018 05:15AM
Subject: Re: [CP2K:9919] SCF_GUESS