LOPTICS + MAGMOM

[giacomo giorgi]

Dear All,
I am performing nowadays some calculations of optical spectra (LOPTICS=.TRUE., NPAR=1...) on a Magnetic system (a MnO in a FM configuration)

While after calculating the band I get a Egap=1.0 eV (that is, the VB is spin up and the CB is SPIN DOWN), the optical spectra (the imaginary part of the epsilon) shows a huge peak well below the gap energy

frequency dependent IMAGINARY DIELECTRIC FUNCTION (RPA, no local field effects)
E(ev) X Y Z XY YZ ZX
--------------------------------------------------------------------------------------
0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000
0.056169 74.928523 75.663974 0.252521 -0.637750 3.467413 -2.003528
0.112339 141.618580 142.207906 0.484692 -0.510799 6.500063 -3.755839
--> 0.168508 161.760045 161.922844 0.589797 -0.140712 7.395751 -4.273387
0.224677 136.274687 136.141501 0.568368 0.115897 6.230580 -3.600128
0.280847 105.444197 105.318658 0.540595 0.109225 4.845358 -2.799729
......
0.842541 18.586362 18.540847 1.144530 0.039511 0.823084 -0.475592
0.898710 14.710207 14.645021 1.003089 0.056577 0.647523 -0.374149
0.954879 12.625128 12.533491 0.936991 0.079518 0.556587 -0.321605
1.011049 11.854132 11.742192 0.939403 0.097137 0.520990 -0.301037
1.067218 11.441409 11.351692 0.949195 0.077864 0.499250 -0.288474
1.123387 10.550490 10.503939 0.894344 0.040408 0.454392 -0.262555
1.179557 9.295434 9.281150 0.809291 0.012410 0.393893 -0.227598
.....

This does not match with my expectation since I would expect such peak at energy corresponding to the Egap. At variance, for values of E close to 1 eV the optical peak tends to decrease...
Of course, bandgap and optical properties are calculated with the same number of k-points (the former with ISMEAR=0, the latter with ISMEAR=-5).

I am getting "crazy" because I am not able to figure out the reason for such behaviour....

Do you know if there is some shortcoming in combining LOPTICS calculations with Magnetic systems?
I attach you the INCAR for the LOPTICS calculation.
I would be very glad and grateful if someone could be able to reply and help me.
I really need it.


Thanks in advance,
Giacomo

SYSTEM = MnO

# xc
GGA = PE
ISTART = 1

#electronic relaxation
LREAL = Auto
PREC= High

ISMEAR = -5
SIGMA = 0.05

NELMIN = 4
NELM = 200

ISIF = 2
ISPIN=2
MAGMOM=4*3.0 8*0.

IBRION = 1

EDIFF = 1.E-5
EDIFFG = -0.01

NGX=44
NGY=44
NGZ=88

NSW = 0

AMIX = 0.2
BMIX = 0.00001
AMIX_MAG = 0.8
BMIX_MAG = 0.00001

LORBIT = 12
ICHARG=11

LOPTICS=.TRUE.
NBANDS=220
NEDOS=2000
NPAR = 1

[user224]

Hi,

A very old post I know, but did you figure this out?

Also if anyone else can comment I'd v much appreciate it..

Thanks!

[quote author=.TRUE., NPAR=1...) on a Magnetic system (a MnO in a FM configuration)

While after calculating the band I get a Egap=1.0 eV (that is, the VB is spin up and the CB is SPIN DOWN), the optical spectra (the imaginary part of the epsilon) shows a huge peak well below the gap energy

frequency dependent IMAGINARY DIELECTRIC FUNCTION (RPA, no local field effects)
E(ev) X Y Z XY YZ ZX
--------------------------------------------------------------------------------------
0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000
0.056169 74.928523 75.663974 0.252521 -0.637750 3.467413 -2.003528
0.112339 141.618580 142.207906 0.484692 -0.510799 6.500063 -3.755839
--> 0.168508 161.760045 161.922844 0.589797 -0.140712 7.395751 -4.273387
0.224677 136.274687 136.141501 0.568368 0.115897 6.230580 -3.600128
0.280847 105.444197 105.318658 0.540595 0.109225 4.845358 -2.799729
......
0.842541 18.586362 18.540847 1.144530 0.039511 0.823084 -0.475592
0.898710 14.710207 14.645021 1.003089 0.056577 0.647523 -0.374149
0.954879 12.625128 12.533491 0.936991 0.079518 0.556587 -0.321605
1.011049 11.854132 11.742192 0.939403 0.097137 0.520990 -0.301037
1.067218 11.441409 11.351692 0.949195 0.077864 0.499250 -0.288474
1.123387 10.550490 10.503939 0.894344 0.040408 0.454392 -0.262555
1.179557 9.295434 9.281150 0.809291 0.012410 0.393893 -0.227598
.....

This does not match with my expectation since I would expect such peak at energy corresponding to the Egap. At variance, for values of E close to 1 eV the optical peak tends to decrease...
Of course, bandgap and optical properties are calculated with the same number of k-points (the former with ISMEAR=0, the latter with ISMEAR=-5).

I am getting "crazy" because I am not able to figure out the reason for such behaviour....

Do you know if there is some shortcoming in combining LOPTICS calculations with Magnetic systems?
I attach you the INCAR for the LOPTICS calculation.
I would be very glad and grateful if someone could be able to reply and help me.
I really need it.


Thanks in advance,
Giacomo

SYSTEM = MnO

# xc
GGA = PE
ISTART = 1

#electronic relaxation
LREAL = Auto
PREC= High

ISMEAR = -5
SIGMA = 0.05

NELMIN = 4
NELM = 200

ISIF = 2
ISPIN=2
MAGMOM=4*3.0 8*0.

IBRION = 1

EDIFF = 1.E-5
EDIFFG = -0.01

NGX=44
NGY=44
NGZ=88

NSW = 0

AMIX = 0.2
BMIX = 0.00001
AMIX_MAG = 0.8
BMIX_MAG = 0.00001

LORBIT = 12
ICHARG=11

LOPTICS=.TRUE.
NBANDS=220
NEDOS=2000
NPAR = 1



[/quote]