Integrated absolute spin density changes significantly during geometry optimization, and is not reproduced in a subsequent SCF run (no smearing)

[Marcella Iannuzzi]

Dear Jannen,

the electrons with antiparallel spin may occupy different orbitals, having 
two singly occupied orbitals. 
Example two separate H atoms with antiparallel spin.
Regards
Marcella


On Sunday, June 10, 2018 at 6:33:35 AM UTC+2, Jannen wrote:
>
> Hello Marcella,
>
> Can I ask a question follow up your explanation? How could the total 
> integrated spin density be not zero when the multiplicity is 1? 
>
> Thanks very much,
> Jannen  
>
> On Friday, January 20, 2017 at 3:03:43 AM UTC-6, Marcella Iannuzzi wrote:
>>
>> Dear Ananth,
>>
>> the total integrated spin density can be different from zero, even if the 
>> multiplicity is stil one, this should not be a problem. 
>> After the geometry optimisation, did you try to restart also the wave 
>> function in addition to the coordinates?
>> I have noticed that in your scf.inp the SCF_GUESS is set to ATOMIC.
>> My guess is that the scf ends to be trapped in a metastable state ,due to 
>> the bad starting guess.
>>
>> Kind regards,
>> Marcella 
>>
>> On Monday, January 16, 2017 at 2:41:56 AM UTC+1, Ananth Govind Rajan 
>> wrote:
>>>
>>> Dear all,
>>>
>>> I am using version 2.5.1 of CP2K for geometry optimizing my system of 
>>> interest, which is a graphene nanoribbon. I have attached the input and 
>>> output files for two separate cases: (a) a geometry optimization 
>>> (geo_opt.inp and geo_opt.out) and (b) an SCF run with the optimized 
>>> geometry (scf.inp and scf.out). Two XYZ files are also attached, the 
>>> initial unoptimized file (zigzag_init.xyz), and the final optimized 
>>> coordinates (optimized_zigzag_initial.xyz) 
>>>
>>> As you will see, I am performing a spin polarized 
>>> (UNRESTRICTED_KOHN_SHAM) calculation, with the MULTIPLICITY set to 1. The 
>>> RELAX_MULTIPLICITY option is not turned on (it is set to zero by default). 
>>> I am *not* using smearing. As the geometry optimization proceeds, the 
>>> integrated absolute spin density (IASD) seems to increase significantly 
>>> (from ~0 to ~18). Is this expected? I would imagine that the IASD is 
>>> related to the specified multiplicity and therefore should not change 
>>> significantly as optimization proceeds, because smearing is not turned on.
>>>
>>> In fact, after geometry optimization finished, I ran a simple SCF run to 
>>> compute the energy of the system using the optimized coordinates. 
>>> Surprisingly, this energy is significantly different (~ 5 eV) than the 
>>> energy obtained at the end of the geometry optimization step, despite 
>>> having similar input files. Moreover, the IASD is also different at the end 
>>> of the SCF run (~ 0), compared to at the end of the GEO_OPT run (~18).
>>>
>>> Can anyone please advise what the issue might be? Why are the results so 
>>> different between the SCF and GEO_OPT? Is it okay that the IASD changes 
>>> during GEO_OPT?
>>>
>>> Please let me know if you need any more information for diagnosing the 
>>> issue.
>>>
>>> Thank you very much
>>>
>>> Best regards,
>>> Ananth Govind Rajan
>>> PhD Candidate
>>> Department of Chemical Engineering, MIT
>>>
>>
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