[CP2K:3575] Re: Is it possible to study/converge magnetic surfaces? repost..

marcella Iannuzzi marc... at pci.uzh.ch
Fri Oct 28 13:37:09 CEST 2011


These are the numbers given before the calculation starts
the number of MOS is obviously unchanged
the total numbe of electrons also,
the number of occupied orbitals and number of electrons per spin are  
based on the multiplicity given from input,
This is used for the initial guess (atomic guess and not for a  
restart), and no more afterwords

marcella

On 28 Oct 2011, at 13:30, Dr. Roman Leitsmann wrote:

> Dear Marcella,
>
> I am a little bit confused.
> I understand your point and I would expect the same behavior.
> However, does this mean that the following lines in the output are not
> reliable in the case of added MOs and applied smearing?
>
>
> For example:
> ...
>
> Spin 1
>
> Number of electrons:			602
> Number of occupied orbitals:		627
> Number of molecular orbitals:		702
>
> Spin 2
>
> Number of electrons:			598
> Number of occupied orbitals:		623
> Number of molecular orbitals:		698
>
> ...
>
> Because at this point always integer numbers are given ...
>
> The other question is how reliable is the population analysis in  
> case of fractional occupied orbitals? Because the total spin moment  
> given in the population analysis is sometimes not in agreement with  
> the above output.
>
> best,
> Roman
>
>
> Am 28.10.2011 12:58, schrieb marci:
>> Dear Roman,
>>
>> For a metallic system it is recommended to use additional MOS and
>> Fermi-Dirac smearing.
>> By doing so within spin-polarized calculations, the total number of
>> electrons per spin channel is not constrained to be an integer  
>> number,
>> because the distribution of the occupation numbers is done on the
>> basis of the energy level of each state with respect to the Fermi
>> energy, irrespective of its spin.
>> The total number of electrons per spin is simply the integral of the
>> charge density associated to that spin.
>> Estimates of the momentum per atom can be obtained by the population
>> analysis
>>
>> Best
>> Marcella
>>
>> On Oct 28, 12:42 pm, "Dr. Roman Leitsmann"<leit... at matcalc.de>
>> wrote:
>>> Dear Marcella,
>>>
>>> I have some (may be stupid) questions about your calculation:
>>>
>>> (1) You are using additional MOs and a certain smearing, right?
>>> However, in the case of fractional charges the computation of the  
>>> spin
>>> moment is not yet proper working in cp2k (WARNING: S** computation  
>>> does
>>> not yet treat fractional occupied orbitals). So my question is:  
>>> How have
>>> you calculated the spin moment.
>>>
>>> (2) How have you calculated the difference between spin up and  
>>> spin down
>>> channel. In my version of cp2k only integer numbers of electrons are
>>> given for each spin channel.
>>>
>>> best
>>> Roman
>>>
>>> Am 28.10.2011 12:20, schrieb marci:
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>> Dear  Valerio
>>>
>>>> I did a second test with a 6x6 slab and 6 layers, and by  
>>>> initializing
>>>> the multiplicity to 131,
>>>> I get a reasonable distribution of spins. Atoms belonging to the  
>>>> same
>>>> layer have all the same spin moment, the outermost layer have the
>>>> largest spin moment 0.66, and the two innermost layer have the  
>>>> lowest
>>>> spin moment 0.56.
>>>> It takes quite a number of iterations (about 140) to converge  
>>>> with a
>>>> convergence criterion of 1E-7.
>>>> I used a mixing parameter of 0.08 and an electronic temperature of
>>>> 2000K.
>>>> The RELAX_MULTIPLICITY keyword is not needed when the smearing is
>>>> used.
>>>> The occupation of the states is attributed according to the Fermi-
>>>> Dirac distribution, through the evaluation of the Fermi energy at  
>>>> each
>>>> SCF step.
>>>> This means that the fractional occupation numbers can change, as  
>>>> well
>>>> as the number of electrons per spin channel, only the total  
>>>> number of
>>>> electrons is constant.
>>>> In the specific case, I monitored the number of electrons per spin
>>>> channel, and it remains quite stable from the beginning to the end,
>>>> though there are some fluctuations, in particular during the first
>>>> iterations.
>>>> The final difference between spin up and spin down is of 131.8
>>>> electrons.
>>>
>>>> best
>>>> Marcella
>>>
>>>> On Oct 26, 4:08 pm, Valerio Bellini<valerio... at unimore.it>
>>>> wrote:
>>>>> Il 26/10/11 15.30, marci ha scritto:
>>>
>>>>>> Dear  Valerio,
>>>
>>>>>> I tried your system, 5x5 Ni(111) slab, and I could converge the
>>>>>> electronic structure by using more or less the same settings  
>>>>>> that were
>>>>>> in your input.
>>>>>> It needs many iterations and the energy keeps oscillating for a  
>>>>>> long
>>>>>> time before the algorithm can find a good minimum.
>>>>>> However, what is really annoying, is that at the end the  
>>>>>> electrons are
>>>>>> redistributed between the two spins in such a way that the final
>>>>>> magnetization is zero, in spite of the fact that the initial  
>>>>>> guess had
>>>>>> a high multiplicity.
>>>>>> It seems that with the present settings and system size, the  
>>>>>> algorithm
>>>>>> finds a minimum with no magnetization, and this should be also  
>>>>>> the
>>>>>> reason why starting from a magnetization different from zero it  
>>>>>> takes
>>>>>> such a long time to converge.
>>>>>> It is possible that one problem is the size of the system. One  
>>>>>> should
>>>>>> check larger boxes to verify that.
>>>>>> What I can tell for sure is that the optimization of the bulk  
>>>>>> (216
>>>>>> atoms) electronic structure, gives the expected magnetization  
>>>>>> (~0.6
>>>>>> magneton per unit cell) by using more or less the same SCF set  
>>>>>> up.
>>>
>>>>>> best
>>>>>> marcella
>>>
>>>>> Dear Marcella,
>>>>> Thank you for the answer.
>>>>> Two comments:
>>>>> 1) I did calculation for the same system, using Gamma point  
>>>>> only, with
>>>>> another code (VASP),
>>>>> and the total magnetic moment of the cell relaxed to around 86  
>>>>> bohr
>>>>> magneton.
>>>>> With a better multiplicity guess I thought convergence might be  
>>>>> easier,
>>>>> but it was
>>>>> not the case.
>>>>> If I try 87 as multiplicity and I run more than 500 iterations  
>>>>> with
>>>>> Broyden,
>>>>> the system converges using Diagonalization+Broyden up to 0.005  
>>>>> Hartree,
>>>>> but as said in the previous e-mail, the magnetic moments are not  
>>>>> equal
>>>>> for different atoms
>>>>> in the same plane, so the system in reality is far from  
>>>>> convergence.
>>>>> Could I ask you how many iterations did it take to you?
>>>>> 2) I do not understand how you could get a non-magnetic solution.
>>>>> If you impose the multiplicity to some value, and you don't allow
>>>>> relaxation of it
>>>>> (using the keyword, RELAX_MULTIPLICITY) the multiplicity of the  
>>>>> system
>>>>> should remain
>>>>> constant (like in a fixed spin moment calculation).
>>>>> So this means that you inserted that flag in the input file, is  
>>>>> that
>>>>> correct?
>>>>> thanks,
>>>>> Valerio
>>>
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>
>
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> AQcomputare GmbH
> Annaberger Strasse 240
>
> 09125 Chemnitz
>
> Telefon:  0371 5347591
> Email:    in... at matcalc.de
> Internet: http://www.matcalc.de
>
> Geschaeftsfuehrer: Dr. Philipp Plaenitz
>
> Gesellschafter:
>   Prof. Dr. Christian Radehaus
>   Dr. Philipp Plaenitz
>
> Amtsgericht Chemnitz: HRB 25386
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