[Wien] extrnal magnetic field effect

[Peter Blaha]

You are absolutely correct, also the magnetic field breaks periodic 
symmetry. In addition, it is even much MORE complicated than an electric 
field, because it is gauge-dependent, (origin) ....

The magnetic field acts an both, the spins (via Vxc up/dn, and this is 
included correctly), and on the orbitals, introducing an orbital current 
and a resulting magnetic field.
The latter is included in this option only in a "single site central 
field (atomic)" approximation in a VERY crude way.

I don't know if this approximation is good enough to give you at least 
roughly the effect you are looking for. Don't expect "quantitative" 
agreement at all.

PS: In the new NMR code, we apply a magnetic field rigorously, but I'm 
afraid only the effect on the wavefunctions (and the resulting current) 
is calculated, but not a change of eigenvalues.

Robert: can you comment on that ??



----------------------------------
Dears Prof. Blaha and Martin Pieper

Thanking you for your reply again

 >Sorry, my mistake. I thought you are using an electric field.

I studied the PRB. 63 165205 (2001) paper, that is about the electric 
field case.

In this paper has been noticed that:

“A general problem in calculating crystal properties in an external 
electric field is that the total potential V =V_int +V_ext  in the 
Hamiltonian” (equation 1)” is no longer periodic. V_int  is the periodic 
potential caused by all charged particles within the crystal, while 
V_ext is the external potential from external charges (outside the 
crystal). The translational symmetry of the wave function is broken and 
from this point of view the solid is no longer an ideal crystal. A 
locally homogeneous external electric field may be simulated by 
introducing a potential with a period several times the lattice 
parameters of the crystal”



And in the section V (DFT CALCULATIONS)

We can see that a supercell and periodic potential to maintain periodic 
boundary condition have been used as V_ext where its Fourier summation 
is Eq.12.

My questions are

Does the external magnetic field change the periodic boundary conditions 
similar to the electric field?

If it does, why do we use the unit cell ?

If it doesn’t, what is the difference between electric and magnetic field?


-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671