[Pw_forum] a question about MnSe

[Mike Mehl]

Two things:

First,

Having atoms designated Mn1 and Mn2 reduces the symmetry from Fm(3-)m 
(cubic rocksalt) to R(-3)m (rhombohedral), which is why you see a 
rhombohedral lattice in the output for the rocksalt structure.

Second,

What answer do you get when you use the primitive cell for the Rocksalt 
structure, rather than one that looks rhombohedral?

CELL_PARAMETERS (cubic)
  0.0 0.5 0.5
  0.5 0.0 0.5
  0.5 0.5 0.0

ATOMIC_POSITIONS (crystal)
Se       0.00 0.00 0.00
Mn       0.50 0.50 0.50


On 01/19/2011 11:57 AM, mohnish pandey wrote:
> Dear QE users,
>                             I am trying to do bulk calculations for MnSe
> in rocksalt and wurtzite structure. Its has AFM ground state in rocksalt
> structure but after checking convergence I am finding "rocksalt"
> structure to be energetically higher than wurtzite structure. I am
> pasting my segments of input and output files. Can anybody please help
> me in figuring out the problem.
>
> *INPUT FOR ROCKSALT*
>
> &control
>      calculation = 'vc-relax'
>      restart_mode='restart',
>      wf_collect = .true.
>      prefix='mnse',
>      pseudo_dir = '/home/mohnish/mnse-rocksalt-bulk',
>      outdir='/home/mohnish/mnse-rocksalt-bulk',
>      tprnfor = .true.,
>      tstress=.true.
>   /
> &system
>      ibrav=  0, celldm(1)= 10.3026, nat=  4, ntyp= 3,
>      ecutwfc = 40.0, ecutrho = 320.0,
>      occupations='smearing', smearing='gauss', degauss=0.01,
>      nspin=2,
>      starting_magnetization(1)= 0.0,
>      starting_magnetization(2)= 0.5,
>      starting_magnetization(3)=-0.5,
>   /
> &electrons
>     diagonalization='david'
>     mixing_mode = 'plain'
>     mixing_beta = 0.4
>     conv_thr = 1.0d-8
>     startingpot = 'file'
>     startingwfc = 'file'
>   /
> &IONS
>    ion_dynamics='bfgs'
>    trust_radius_max = 0.40
>    trust_radius_ini = 0.20
> /
> &CELL
>    cell_dynamics='bfgs',
> /
> ATOMIC_SPECIES
>    Se  78.960 Se.pbe-van.UPF
>    Mn1 54.938 Mn.pbe-sp-van_mit.UPF
>    Mn2 54.938 Mn.pbe-sp-van_mit.UPF
> CELL_PARAMETERS
> 0.50 0.50 1.00
> 0.50 1.00 0.50
> 1.00 0.50 0.50
> ATOMIC_POSITIONS {crystal}
>   Se  0.25 0.25 0.25
>   Se  0.75 0.75 0.75
>   Mn1 0.0  0.0  0.0
>   Mn2 0.5  0.5  0.5
> K_POINTS {automatic}
> 6 6 6 0 0 0



-- 
Michael J. Mehl
Head, Center for Computational Materials Science
Naval Research Laboratory Code 6390
Washington DC