[Wien] [EXTERNAL] Re: YCo5 magnetic anisotropy calculations with GGA+U on Co

[Peter Blaha]

Initially I executed calculation in the "spirit of force theorem" with 
just one iteration and obtained well converged K value calculated from 
EIGEN. However reviewer mentioned that force theorem is not obeyed in 
case of +U calculation - corrections are not in second order. He is 
right, the K value obtained from full scf calculations and total energy 
difference is ~40% higher. For just GGA both approaches gives the same 
result.
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This depends on how you start the EIGN calculation. From a scalar 
relativistic GGA+U calculation or just from GGA ??

And in addition it is probably again a problem of symmetry. Reliable 
values can only be obtained with identical symmetry in the scalarel and 
SO calculation. So you have to perform the scalarel. calc with the same 
struct file (symmetry operations) and case.in2c (LM combinations) as the 
2 SO calculations.

It is NOT only a matter of k-points and cannot be "fixed by x kgen -fbz
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What surprises me is the non-monotonic dependence of K value as a number 
of k-points. At the same time K calculated from the total energy 
converged. While, the  band structure energy is part of the total energy.
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Not a big surprise. During the scf cycle the potential changes. 
Remember, by adding a constant potential, the EIGEN values would change 
by shift*NE, but the potential energy would also shift in opposite 
direction by -shift*NE, so Etot remains constant, but EIGEN not. (NE .. 
number of electrons)

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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300
Email: peter.blaha at tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at
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