[Pw_forum] RE : Noncolin vs Nspin=1 for Chromium

[BARRETEAU Cyrille]

You can only use lspinorbit=.true. if you have a relativistic pseudo which not the case of my pseudo... 
In any case I do not think spin-orbit coupling will change very much your bulk modulus.
SOC is just a tiny effect on total energy, at least for 3d metals...

The most important thing is that you describe properly the AF state. Why do you initialize the magnetization with
starting_magnetization(1)=0.7,
starting_magnetization(2)=-0.4,
breaking the symmetry between the two atoms.
Furthermore you have declared only one type of atoms while you have two types..
I guess you will endup with the non-magnetic solution in your case..

You should declare ntype=2
and
starting_magnetization(1)=0.3,
starting_magnetization(2)=-0.3,


hth
cyrille

-----------------------------------------------------------------------------------------------------------
Cyrille Barreteau
CEA Saclay, IRAMIS, SPCSI, Bat. 462
91191 Gif sur Yvette Cedex, FRANCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
phone:    +33 (0)1 69 08 29 51 / +33 (0)6 47 53 66 52
fax :       +33 (0)1 69 08 84 46
email:     cyrille.barreteau at cea.fr
Web:     http://iramis.cea.fr/Pisp/cyrille.barreteau/
 -----------------------------------------------------------------------------------------------------------

________________________________________
De : pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] de la part de Ben Palmer [benpalmer1983 at gmail.com]
Date d'envoi : jeudi 6 juin 2013 18:27
À : PWSCF Forum
Objet : [Pw_forum] Noncolin vs Nspin=1 for Chromium

Hi Everyone,

I've been using a few of the supplied PPs and one kindly suggested/sent
to me by Derek/Cyrille.  I've used these to try to calculate the bulk
modulus.  First, I used nspin = 1 and with the latest PP ended with a
bulk modulus of 268GPa.  I then repeated with noncolin=.true. and
lspinorb=.true. and I was expecting a different result, but at the end
it gave me 268GPa again.  I was just wondering whether I'd missed
something in my input script, or whether I'd made any obvious errors?

This is one of my nspin=1 input files:

&CONTROL
restart_mode='from_scratch',
calculation=scf,
etot_conv_thr=1.0E-7,
forc_conv_thr=1.0D-6,
nstep=200,
prefix="7ca5bad5d48c",
pseudo_dir="/gpfs/bb/bxp912/pseudopotentials/",
outdir="/gpfs/bb/bxp912/scratch/",
/
&SYSTEM
ibrav=14,
celldm(1)=5.36800113,
celldm(2)=1,
celldm(3)=1,
celldm(4)=0,
celldm(5)=0,
celldm(6)=0,
nat=2,
ntyp=1,
ecutwfc=600,
ecutrho=2400,
occupations='smearing',
smearing='mv',
degauss=0.1,
/
&ELECTRONS
diagonalization='david',
mixing_mode='plain',
mixing_beta=0.7,
conv_thr=1.0D-7,
/
&IONS
ion_dynamics='bfgs',
/
&CELL
cell_dynamics='bfgs',
press=0.0,
cell_factor=2.0,
/
ATOMIC_SPECIES
Cr 51.9961 Cr.pbe-us_norel_cyrille.UPF
ATOMIC_POSITIONS crystal
Cr 0.0000000000 0.0000000000 0.0000000000
Cr 0.5000000000 0.5000000000 0.5000000000
K_POINTS automatic
8 8 8 1 1 1

And this is one of my noncolin input files:

&CONTROL
restart_mode='from_scratch',
calculation=scf,
etot_conv_thr=1.0E-7,
forc_conv_thr=1.0D-6,
nstep=200,
prefix="c7700ccaacf",
pseudo_dir="/gpfs/bb/bxp912/pseudopotentials/",
outdir="/gpfs/bb/bxp912/scratch/",
/
&SYSTEM
ibrav=14,
celldm(1)=5.4753116928,
celldm(2)=1,
celldm(3)=1,
celldm(4)=0,
celldm(5)=0,
celldm(6)=0,
nat=2,
ntyp=1,
ecutwfc=400,
ecutrho=1200,
occupations='smearing',
smearing='mv',
degauss=0.1,
noncolin=.true.,
lspinorb=.true.,
starting_magnetization(1)=0.7,
starting_magnetization(2)=-0.4,
/
&ELECTRONS
diagonalization='david',
mixing_mode='plain',
mixing_beta=0.7,
conv_thr=1.0D-7,
/
&IONS
ion_dynamics='bfgs',
/
&CELL
cell_dynamics='bfgs',
press=0.0,
cell_factor=2.0,
/
ATOMIC_SPECIES
Cr 51.9961 Cr.pbe-us_norel_cyrille.UPF
ATOMIC_POSITIONS crystal
Cr 0.0000000000 0.0000000000 0.0000000000
Cr 0.5000000000 0.5000000000 0.5000000000
K_POINTS automatic
8 8 8 1 1 1

All the best,

Ben

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