[Pw_forum] Energy convergence in Cobalt

[Conor Hogan]

Dear forum,

I was trying to find the right kinetic energy cut-off using PWscf
for a molecule which contains a cobalt atom.
I already tested the convergence for the same molecule without cobalt,
and everything seems fine.

Now I am testing the kinetic energy cut-off with cobalt.
The pseudo is : Co.pz-nd-rrkjus.UPF downloaded from the web

For this reason I performed scf calculations, varying the cut-off  both 
for an isolated Cobalt atom and also for the hexagonal bulk phase of
Cobalt.

In both cases I noted that the total energy does not decrease
if the kinetic energy cut-off is increased, which is not what
I expected (in fact it increases!)

Here the results:

Isolated atom:

ecut=30 ry etot= -73.7557 ry
ecut=40 ry etot= -73.7430 ry
ecut=50 ry etot= -73.7367 ry

Bulk of Co:

ecut  30  -148.4497 ry
ecut  40  -148.4448 ry
ecut  50  -148.4440 ry

I guess I am doing something stupid in the input - perhaps
someone has an idea why? Am I missing convergence with respect to another
parameter perhaps?

The same problem happens with a PBE Co-pseudo downloaded from the web so I
don't think it is a problem with the pseudopotential..!
 
Cheers
Conor
 
Here are the two input files:

Input for ISOLATED Co Atom:

    calculation = 'scf'
    restart_mode='from_scratch'
    verbosity= 'high',
    prefix='Co2',
    pseudo_dir = 'pseudo',
    max_seconds=1000,
    disk_io='minimal',
    etot_conv_thr=1.0e-5
    outdir='./'
 /
 &system
    ibrav= 8, celldm(1)=20., celldm(2) =1, celldm(3) = 1.
    nat=1, ntyp=1, nbnd=30,
    nelec = 9.00, nosym=.true.
    nelup = 6
    neldw = 3
    nspin = 2,
    starting_magnetization = 1.0 ,
    ecutwfc = 50.0
    occupations='fixed'
 /
 &electrons
 diago_thr_init=1.0e-3
 electron_maxstep = 200,
 conv_thr  = 1.e-7, mixing_beta =0.6
 /
ATOMIC_SPECIES
Co  58.00  Co.pz-nd-rrkjus.UPF
ATOMIC_POSITIONS (angstrom)
Co      5. 5. 5.
K_POINTS (gamma)

Input for Co-BULK:
-----------------

 &control
    calculation = 'scf'
    restart_mode='from_scratch'
    verbosity= 'high',
    prefix='Co-bulk',
    pseudo_dir = 'pseudo',
    max_seconds=1000,
    disk_io='minimal',
    etot_conv_thr=1.0e-5
    outdir='./'
 /
 &system
    ibrav= 4, celldm(1)=4.74480009, celldm(2) =1, celldm(3) = 1.600000
nat=2, ntyp=1
    nspin = 2,
    starting_magnetization(1) = 1.0 ,
    ecutwfc = 40.0
    occupations='smearing', smearing='gaussian' , degauss=0.001
 /
 &electrons
 diago_thr_init=1.0e-3
 electron_maxstep = 200,
 conv_thr  = 1.e-7, mixing_beta =0.6
 /
ATOMIC_SPECIES
Co  58.00  Co.pz-nd-rrkjus.UPF
ATOMIC_POSITIONS (crystal)
Co        0.0000000   0.0000000   0.00000000
Co        0.6666667   0.3333333   0.50000000
K_POINTS (automatic)
 10 10 10 0 0 1




Maurizia Palummo

Dipartimento di Fisica
Universita' 'Tor Vergata'
Via della Ricerca Scientifica I
tel.++39-06-72594894
fax ++39-06-2023507
www.fisica.uniroma2.it/palummo