Problems obtaining EOS  [SOLVED]

structure determination,...

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Problems obtaining EOS

Postby AntonF » Wed Feb 06, 2019 1:52 pm

Dear all,

I'm trying to perform an equation of state calculation for FeSi compound with the following input
Code: Select all
ndtset   8
getwfk -1

#Definition of the unit cell
acell1   3*0.938
acell2   3*0.954
acell3   3*0.960
acell4   3*0.968
acell5   3*0.974
acell6   3*0.981
acell7   3*0.987
acell8   3*0.993

    rprim       8.507000000       0.000000000       0.000000000   
                0.000000000       8.507000000       0.000000000   
                0.000000000       0.000000000       8.507000000

#Definition of the atom types
   ntypat  2         # There are two types of atom
   znucl   26 14     # The keyword "znucl" refers to the atomic number of the
                      # possible type(s) of atom. The pseudopotential(s)
                      # mentioned in the "files" file must correspond
                      # to the type(s) of atom.

#Definition of the atoms
    natom   8         # There are eight atoms
    typat   1 1 1 1 2 2 2 2
                       
     xred   0.00000000    0.00000000    0.00000000
            0.23200000    0.73200000    0.50000000
            0.50000000    0.23200000    0.73200000
            0.73200000    0.50000000    0.23200000
            0.71050000    0.71050000    0.71050000
            0.52150000    0.02150000    0.21050000
            0.21050000    0.52150000    0.02150000
            0.02150000    0.21050000    0.52150000

#Definition of the planewave basis set
ecut  10.0         # Maximal kinetic energy cut-off, in Hartree

#Exchange-correlation functional
ixc 1             # LDA Teter Pade parametrization

#Definition of the k-point grid
kptopt 1          # Option for the automatic generation of k points, taking
                  # into account the symmetry
ngkpt 8 8 8       # This is a 8x8x8 FCC grid, based on the primitive vectors

toldfe 1.0d-8     # Will stop when, twice in a row, the difference
                  # between two consecutive evaluations of total energy
                  # differ by less than toldfe (in Hartree)
                  # This value is way too large for most realistic studies of materials
diemac 10

and with psp8 pseudopotentials downloaded from the Abinit website. However, instead of a smooth curve with a minimum I get something like
https://thumb.cloud.mail.ru/weblink/thumb/xw1/4kYB/rpc3mnD35/fesi.JPG?x-email=undefined
I have tried different pseudopotentials, ngkpt and ecut parameters seem to be high enough.
Any comments are welcome

Thank you in advance,
Anton F.
AntonF
 
Posts: 3
Joined: Fri Feb 01, 2019 8:53 am

Re: Problems obtaining EOS  [SOLVED]

Postby ebousquet » Mon Feb 11, 2019 4:33 pm

Dear Anton,
I'm almost 100% sure that ecut=10 Ha is clearly not enough for norm-conserving pseudos... The psp8 from pseudodojo usually requires 30-50 Ha.
All the best,
Eric
ebousquet
 
Posts: 248
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

Re: Problems obtaining EOS

Postby AntonF » Fri Feb 22, 2019 12:14 pm

Dear Eric,
Thank you for your advice! Indeed, increasing ecut up to 30 Ha sufficiently improved the results. I was underestimating these pdeudos.
Best wishes,
Anton.
AntonF
 
Posts: 3
Joined: Fri Feb 01, 2019 8:53 am


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