[Wien] PHONON calculations with spin-orbit coupling

[Seyed Javad Hashemifar]

I think the first criteria is that dx should not be so small that the
resulting dE become comparable or smaller than energy accuracy of your
system. Or other way around, the energy accuracy of your calculation should
be considerably larger than dE, it means that if you reduce dx, then
accuracy (kpoints, rkmax, convergency) should be increased consistently.

Javad Hashemifar

2009/7/14 Atta-fynn, Raymond <attafynn at uta.edu>

>  Dear WIEN2k users and authors,
>
> As it stands, the Hellmann-Feynman forces cannot be computed when
> spin-orbit coupling (SOC) is present. I want to compute the phonon
> dispersion relations for an fcc cell using PHONON but I want to use SOC
> forces so I intend to compute the forces on the atoms using the SOC total
> energies. The force on a single atom along a coordinate direction, say
> x, will be calculated as
>
> Fx_i = del_E/(2*dx), where del_E = Etot (x_i + dx) - Etot (x_i - dx)
>
> Following the above procedure for an fcc cell with 4 inequivalent atoms, 8
> total energy calculations will be carried out for each structure (assuming I
> want forces along the x-direction only).
>
> My concern is how to choose a "good value" of dx that will yield forces
> accurate to within 0.1 mRy/Bohr. My guess is dx = 0.01 Bohr but I would like
> to seek some input from other users before I proceed with the
> calculations. Also, should the total energy be computed to a higher degree
> of accuracy, say 8 or 9 decimal places?
>
> Thank you.
>
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>


-- 
======================================
Seyed Javad  Hashemifar
Physics Department, Isfahan University of Technology
84156-83111 Isfahan, Iran
Tel: +98 311 391 2375     Fax:+98 311 3912376
Email:  hashemifar at cc.iut.ac.ir
Homepage:  http://hashemifar.iut.ac.ir
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