Spin Spirals

Message

manish_jain · #1 Post by **manish_jain** » Thu Apr 14, 2005 5:24 pm

Hello All,

I was wondering if anyone has used spin spirals in VASP. I know that they are not officially supported - but I need to use them.

All I found was the following:
LSPIRAL, QSPIRAL - first one I assume is the flag for turning spirals on and second one gives the direction of the spin spiral vector.

Besides specifying these, LNONCOLLINEAR, and initial moments with MAGMOM, is there anything else that I need to do? I am assuming that the best way to go about this is first do a non spin polarized calculation and then a spin polarized one with these specified (just as for regular non-collinear calculations)

Any comments or documentation for them will be greatly appreciated.

Thanks,
Manish

#2 Post by **admin** » Fri Apr 22, 2005 2:32 pm

set:
ISYM = -1
ISPIN = 2
LNONCOLLINEAR = .TRUE.
LASPH = .TRUE.
LSPIRAL = .TRUE.
QSPIRAL = propagation vector of the spiral in direct coordinates of the
reciprocal lattice
it might be necessary to re-compile with the precompiler flags
use_enini_without_ldelay
E_cutoffs: to provide spherical FT-components for
spin-up (k+q) and
spin_down (k-q)
set ENCUT high and enini lower (by about 100 eV)

Anonymous · #3 Post by **Anonymous** » Fri Apr 22, 2005 5:23 pm

Thanks. This helps.

Manish

mqian · #4 Post by **mqian** » Wed Jul 06, 2005 9:41 pm

I also try to calculate the SS case.
May I ask the question?
QSPIRAL is set by using direct or cart coordinates??

Thanks a lot!

#5 Post by **admin** » Fri Jul 08, 2005 9:52 am

please read the reply above more carefully: direct coordinates

mqian · #6 Post by **mqian** » Thu Jul 14, 2005 8:35 pm

Hi, I am testing the gamma-Fe as in PRB 66, 224409(2002) by M. Marsman.
But I can not reproduce its results.
In particular, I found that the total energy is dependent
on the initial direction of magnetic moment located in the xy-plane.
( I set the axis of spin spiral as the z-direction)
Moreover, at q=\Gamma I can not reproduce the result of FM.
Would you please give any suggestions?

Here is my INCAR: (CHGCAR for PM has been calculated separately)

System = gammaFe

ICHARG = 1
ISMEAR = -5
PREC = High
ENCUT = 500
EDIFF = 1E-6
GGA = PE
VOSKOWN = 1
ISPIN = 2

ISIM = -1
LNONCOLLINEAR = .TRUE.
LSPIRAL = .TRUE.
QSPIRAL = 0.1 0.1 0.0 ( i.e. q=(0, 0, 0.2) 2*Pi/a )
LASPH = .TRUE.
MAGMOM = 3 3 0

LWAVE = .FALSE.
LCHARG = .TRUE.

NEDOS = 901

POSCAR:Fe fcc
3.5695
0.0000000000000000 0.5000000000000000 0.5000000000000000
0.5000000000000000 0.0000000000000000 0.5000000000000000
0.5000000000000000 0.5000000000000000 0.0000000000000000
1
Direct
0.0000000000000000 0.0000000000000000 0.0000000000000000

TESTING RESULTS:

Case 1 M330
( Mx, My and Mz are 3.0, 3.0 and 0.0 Bohr magnetons respectively)
#q F F(ASPH) Mx My Mz |M|
0.0 -.82029869E+01 -.82140285E+01 1.7060 1.7062 0.0000 2.41279
0.2 -.81971620E+01 -.82074951E+01 1.6497 1.6497 0.0000 2.33303
0.4 -.81998983E+01 -.82076132E+01 1.4432 1.4432 0.0000 2.04099
0.6 -.81958420E+01 -.82016030E+01 1.2820 1.2820 0.0000 1.81302
0.8 -.81673789E+01 -.81732868E+01 1.1238 1.1238 0.0000 1.58929
1.0 -.81496718E+01 -.81560258E+01 0.9917 0.9917 0.0000 1.40248

Case 2 M500
#q F F(ASPH) Mx My Mz |M|
0.0 -.83071696E+01 -.83330020E+01 2.3200 -0.0007 0.0000 2.32
0.2 -.83305941E+01 -.83549166E+01 2.2792 0.0000 0.0000 2.2792
0.4 -.84064368E+01 -.84274399E+01 2.1828 0.0000 0.0000 2.1828
0.6 -.85044384E+01 -.85232690E+01 2.0109 0.0000 0.0000 2.0109
0.8 -.85938784E+01 -.86111871E+01 1.8210 0.0000 0.0000 1.821
1.0 -.86957744E+01 -.87105442E+01 1.7308 0.0000 0.0000 1.7308

In physics, they should give the same results
if I did not consider SO coupling and there is the same cone angle.

Does anybody have experience of Spin Spiral calculations?
Please give any suggestions and comments!

Thanks in advance!

Qian

wbutler · #7 Post by **wbutler** » Mon Jun 26, 2006 2:42 am

I have an additional question about spin sprials. How is the amplitude of the spiral set? We have instructions for setting the wavelength. But not (so far as I can tell) the amplitude.