[Pw_forum] occupation

Matteo Cococcioni matteo at umn.edu
Thu Jul 30 20:18:35 CEST 2009


the new tutorial on the calculation of U can be downloaded from this 
webpage:

http://www.quantum-espresso.org/wiki/index.php/QESB09#First_week


Matteo Cococcioni wrote:
> Dear Ali,
>
> on the wiki page of quantum-espresso you should be able to find a new 
> tutorial on the calculation of U. Please download it
> and run the scripts in there following the instructions.
>
>
>
> ali kazempour wrote:
>   
>> Dear all
>>
>> From Linear response calculation ,I get for TiO2 bulk U=5.73, But when 
>> I double the unit cell in z direction and again compute U ,I get three 
>> different value for Ti atoms.(U=5.63,5.46,5.70).
>>
>>     
>
> what are these three values? I assume they are what you get with 
> supercells of three different sizes. is this correct? if it is the only 
> strange thing is that the intermediate value is lower than the other 
> two. otherwise you got pretty nice convergence of U which is what you 
> want to achieve. Is there any particular reason (apart computational 
> cost) why you only enlarge the cell in z direction?
>
>   
>> Why these values are not same . what is the main reason? Does it in 
>> numerical variation errors?
>> ANother question:
>> When we perturb D level by alpha, it give rise to change in d 
>> occupancy . Is it correct that if we impose negative alpha , the 
>> occupation becomes less than initial state .?
>>
>>     
>
> no. positive alpha -- > decrease in total n. but you need to look at the 
> right n....
>
>   
>> for Ti isolated atom for apha=0.1  tr[ns(na)] after first-iteration 
>> equal to the 0.002 and at the end of calculation is 2.327 while we 
>> know that for Ti,  tr[ns(na)] =2.000. Does it seems to be correct.?
>>
>>      Number of iteration with fixed ns =  0
>>      Starting ns and Hubbard U :
>>  enter write_ns
>> U( 1) =  0.0000
>> alpha( 1) =  0.1000
>> atom  1   Tr[ns(na)]=   2.0000000
>> atom  1  spin  1
>> eigenvalues:  0.4000000 0.4000000 0.4000000 0.4000000 0.4000000
>>  eigenvectors
>>  1   1.0000000  0.0000000  0.0000000  0.0000000  0.0000000
>>  2   0.0000000  1.0000000  0.0000000  0.0000000  0.0000000
>>  3   0.0000000  0.0000000  1.0000000  0.0000000  0.0000000
>>  4   0.0000000  0.0000000  0.0000000  1.0000000  0.0000000
>>  5   0.0000000  0.0000000  0.0000000  0.0000000  1.0000000
>>  occupations
>>  0.400  0.000  0.000  0.000  0.000
>>  0.000  0.400  0.000  0.000  0.000
>>  0.000  0.000  0.400  0.000  0.000
>>  0.000  0.000  0.000  0.400  0.000
>>  0.000  0.000  0.000  0.000  0.400
>> atom  1  spin  2
>> eigenvalues:  0.0000000 0.0000000 0.0000000 0.0000000 0.0000000
>>  eigenvectors
>>  1   1.0000000  0.0000000  0.0000000  0.0000000  0.0000000
>>  2   0.0000000  1.0000000  0.0000000  0.0000000  0.0000000
>>  3   0.0000000  0.0000000  1.0000000  0.0000000  0.0000000
>>  4   0.0000000  0.0000000  0.0000000  1.0000000  0.0000000
>>  5   0.0000000  0.0000000  0.0000000  0.0000000  1.0000000
>>  occupations
>>  0.000  0.000  0.000  0.000  0.000
>>  0.000  0.000  0.000  0.000  0.000
>>  0.000  0.000  0.000  0.000  0.000
>>  0.000  0.000  0.000  0.000  0.000
>>  0.000  0.000  0.000  0.000  0.000
>> nsum =   2.0000000
>>  exit write_ns
>>
>>     
>
> this is not the first iteration. this is what the initial guess of the 
> on-site occupations the code does to start the calculation
>
>
>   
>>  Atomic wfc used for LDA+U Projector are NOT orthogonalized
>>      Starting wfc are    9 atomic +    1 random wfc
>>
>>      total cpu time spent up to now is     13.34 secs
>>
>>      per-process dynamical memory:   326.3 Mb
>>
>>      Self-consistent Calculation
>>
>>      iteration #  1     ecut=    45.00 Ry     beta=0.70
>>      CG style diagonalization
>>      c_bands:  3 eigenvalues not converged
>>      c_bands:  2 eigenvalues not converged
>>      ethr =  1.00E-12,  avg # of iterations = 40.4
>>  enter write_ns
>> U( 1) =  0.0000
>> alpha( 1) =  0.1000
>> atom  1   Tr[ns(na)]=   0.0021401
>> atom  1  spin  1
>> eigenvalues:  0.0000001 0.0000001 0.0000001 0.0009883 0.0009883
>>  eigenvectors
>>  1   0.0000000 -0.8803392 -0.4743427  0.0000000  0.0013927
>>  2   0.0000000 -0.4743432  0.8803400  0.0000000 -0.0000040
>>  3   0.0000000  0.0012242  0.0006642  0.0000000  0.9999990
>>  4  -0.8886820  0.0000000  0.0000000 -0.4585240  0.0000000
>>  5   0.4585240  0.0000000  0.0000000 -0.8886820  0.0000000
>>  occupations
>>  0.001  0.000  0.000  0.000  0.000
>>  0.000  0.000  0.000  0.000  0.000
>>  0.000  0.000  0.000  0.000  0.000
>>  0.000  0.000  0.000  0.001  0.000
>>  0.000  0.000  0.000  0.000  0.000
>>
>>     
>
> this is the first iteration! the problem is, in my opinion, that you 
> didn't start this calculation from wfc and potential saved from the scf 
> unperturbed run, but from scratch (that's why the code has to make the 
> initial guess for the n).
>
> regards,
>
> Matteo
>   
>> ---------------------------------- and end of the file is
>> :
>>      End of self-consistent calculation
>>  enter write_ns
>> U( 1) =  0.0000
>> alpha( 1) =  0.1000
>> atom  1   Tr[ns(na)]=   2.3270531
>> atom  1  spin  1
>> eigenvalues:  0.1574294 0.1574294 0.1574294 0.9273825 0.9273825
>>  eigenvectors
>>  1   0.0000000 -0.4359030 -0.7986559  0.0000000  0.4148945
>>  2   0.0000000  0.7269732 -0.0406891  0.0000000  0.6854592
>>  3   0.0000000 -0.5305643  0.6004109  0.0000000  0.5983379
>>  4  -0.9258933  0.0000000  0.0000000 -0.3777851  0.0000000
>>  5   0.3777851  0.0000000  0.0000000 -0.9258933  0.0000000
>>  occupations
>>  0.927  0.000  0.000  0.000  0.000
>>  0.000  0.157  0.000  0.000  0.000
>>  0.000  0.000  0.157  0.000  0.000
>>  0.000  0.000  0.000  0.927  0.000
>>  0.000  0.000  0.000  0.000  0.157
>>
>>
>> Ali Kazempour
>> Physics department, Isfahan University of Technology
>> 84156 Isfahan, Iran. Tel-1: +98 311 391 3733
>> Fax: +98 311 391 2376 Tel-2: +98 311 391 2375
>>
>>
>> ------------------------------------------------------------------------
>>
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>>   
>>     
>
>
>   


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Matteo Cococcioni
Department of Chemical Engineering and Materials Science,
University of Minnesota
421 Washington Av. SE
Minneapolis, MN 55455
Tel. +1 612 624 9056    Fax +1 612 626 7246
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