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

[Jannen]

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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