[Pw_forum] how to fix the occupations in DFT+U

[simone marocchi]

Dear all, I am simulating compounds with rare earths within a collinear
calculation. I tried to suggest some occupations of the f orbitals for the
Tb atom, using the starting_ns_eigenvalue(m,ispin,I). Unfortunately also
with a small value of electronic mixing and big values of U, the imposed
occupations was lost during the iterative cycle. So I used also
mixing_fixed_ns > electron_maxstep. Also in this case after I obtain the
total energy convergence the density matrix of the last iteration is
different to the one imposed in the input_file.
Can someone of you kindly explain me how the mixing_fixed_ns works ? Do it
uses a sort of Lagrange multipliers to force the occupations or is more
like a penalty function ? Finally, is it possible to work around the
problem, converging to a determined occupation ?

Thanks in advance for every suggestion,

Simone Marocchi

S3 Center, Istituto Nanoscienze, CNR
via Campi 213/A, 41125, Modena, Italy
Tel: +39 *0592055585*;  Skype: jacobi84
URL: http://www.nano.cnr.it
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