Spin Contamination

[mario...@gmail.com]

Dear CP2K Community,

I have not managed to find a keyword to print out the spin contamination for radicals. I've tried keywords which have been mentioned in various threads within this forum, but I've been unsuccessful. Is there a specific keyword or maybe it is available for only specific methods?

Best Regards,

Mario

[Matt W]

By default you should get information of the form

  Integrated absolute spin density  :                               1.2873281839

  Ideal and single determinant S**2 :                    0.750000       0.761094

at the end of a spin polarized SCF cycle. There is no spin purification or other methods available.

Matt

[mario...@gmail.com]

Dear Matt,

Thank you for your anwser. That was my initial expectation as well, but for some reason my output does not contain the lines. I suspect that I am missing something in my input, would it be possible for your to go over it, I attached it with this post?

It is a methoxy radical (something simple to understand how the input works). I did try to add the "multiplicity" keyword as well, but it seems that it is not necessary for this specific system as the results are the same.

Thank You in Advance,

Mario

---------

&GLOBAL
  PROJECT OPT
  RUN_TYPE GEO_OPT
  PRINT_LEVEL LOW
&END GLOBAL
&FORCE_EVAL
  METHOD QS
  &DFT
    &POISSON
      PERIODIC NONE
    &END POISSON
    UNRESTRICTED_KOHN_SHAM TRUE
     &QS
       METHOD AM1
     &END QS
     &SCF
       SCF_GUESS ATOMIC
       MAX_SCF 300
     &END SCF
  &END DFT
  &SUBSYS
    &CELL
      ABC 50.0 50.0 50.0
      PERIODIC NONE
    &END CELL
    &COORD
      O       -6.7915710219      0.8550291655      0.3707621229
      C       -6.3610047229      2.0733410731     -0.0278225846
      H       -5.2321940112      2.0805647692     -0.0050313906
      H       -6.7167364006      2.8433470227      0.7171003965
      H       -6.7222180465      2.3418648071     -1.0550067632
    &END COORD
  &END SUBSYS
&END FORCE_EVAL
&MOTION
  &GEO_OPT
   MAX_ITER 300
  &END GEO_OPT
&END MOTION

---------

[Matt W]

Maybe print level medium?

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

Hi

My guess:

&QS
METHOD AM1
&END QS

Nobody cared to implement this for semi-empirical methods.

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: "Matt W"
Sent by: cp...@googlegroups.com
Date: 12/03/2020 03:29PM
Subject: [CP2K:14337] Re: Spin Contamination

--
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+uns...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cp2k/9399ea60-8594-4305-a4d7-66cd38eeb862n%40googlegroups.com.

[mario...@gmail.com]

Dear Matt and Juerg,

I tried both MEDIUM and HIGH print levels, it does not appear there. It is an interesting guess, because I do get a lot of warning messages with the higher print level which suggest that multiple operations are not implemented in semi-empirical calculations. I'll try the same input with another method to see if it works or not.

Best Regards,

Mario

[mario...@gmail.com]

It seems that Juerg was right, it is not implemented for semi-empirical methods. The information about spin contamination became available right after I changed AM1 to the XC functional PBE.

Thank you both for your input. Would you think this is something the developers would be interested in adding in?

Best Regards,

Mario

[mario...@gmail.com]

For anyone who reads this thread! It seems that it is possible to calculate the spin contamination value manually. One needs to include the eigenvectors into the CP2K output by adding the PRINT statement to the DFT block and print out the eigenvectors (https://manual.cp2k.org/cp2k-6_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/PRINT/MO.html#EIGENVECTORS). I also specified the multiplicity of the calculation explicitly in the input.

The equation for the calculation of spin contamination is described here: https://en.wikipedia.org/wiki/Spin_contamination . And the eigenvectors are used to calculate the last term in the equation - I believe it is the sum of the overlap between the occupied alpha and beta orbitals. The overlap can be found by multiplying each alpha eigenvector with the corresponding beta eigenvector and then adding the results together.

I added an example of how to do it as an attachment.

Best Regards,

Mario