[Wien] Question on spin-orbit coupling calculation

[hyunjung kim]

Dear all,

I have some question on calculation including spin-orbit coupling (SOC). 

In according to the manual, the second-variational procedure requires to include many more unoccupied states to be calculated. And it can be controlled by increasing the energy maximum (Emax) which eigenvalues shall be searched. 

For the Emax which defines the number of eigenvalues to be calculated, I have used Emax=2.5 Ry in non-SOC and 5.0 Ry for SOC. Thus, the number of eigenvalues in SOC calculation were increased by about 2 times larger than that of non-SOC. And also I have check the convergence in the function of Emax value. For non-SOC calculations, it does not depend on Emax value as expected. However in the case of SOC calculations, total energy was depend on the Emax value. Larger Emax results the total energy go down. But up to 10Ry of Emax, I cannot find convergence in total energy. You can find the numbers below.

system : Bismuth bulk (including SOC) ; total energy
Emax = 2   ; E(total) =  -86326.2333  Ry
Emax = 2.5 ; E(total) =  -86326.2420  Ry
Emax = 3   ; E(total) =  -86326.2454  Ry
Emax = 4   ; E(total) =  -86326.2527  Ry
Emax = 5   ; E(total) =  -86326.2577  Ry
Emax = 7   ; E(total) =  -86326.2634  Ry
Emax = 10  ; E(total) =  -86326.2662  Ry


Questions are,
1. Why the unoccupied states affect the total energy in the case of SOC been included?
2. Is there appropriate suggestions taking Emax value?
3. Should the total energy converged as the function of Emax?
4. Within same Emax restriction (i.e. same parameters), could the total energy be compared between different geometries? 

Thank you.
Best regards,
Hyun-Jung Kim.



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Hyun-Jung Kim (Ph.D student)	| phone : ++82 10 7335 7889
Department of Physics		| 
Hanyang University		| e-mail: angpangmokjang at hanmail.net 
17 Haengdang-Dong		| 
133-791 Seongdong-Ku,Seoul/Korea|
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	    www: http://physics.hanyang.ac.kr/~sst/
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