Running Birch Murnaghan

Message

jess · #1 Post by **jess** » Wed Feb 08, 2012 1:01 am

Hello all,

How to run the Birch murnaghan in Vasp?

Thank you for your help !!

Danny · #2 Post by **Danny** » Wed Feb 08, 2012 4:11 pm

1) write a script to run the required set of calclations (i.e. with varying Volume
2) collect data as E/Vol
3) write program to fit BM-Equation of state to E/Vol data

Danny

vistawanted · #3 Post by **vistawanted** » Wed Feb 08, 2012 6:50 pm

By fixing the atoms fraction positon and calculating total energy at different lattice parameters, you can get the volume vs energy curve, which can be fitted to B-M EOS.
If you wanna avoid the trouble to write program by yourself, the eos utility in ELK or Exciting code is a good choice. Or, you can choose the simpler one, ev.x in Quantum-ESPRESSO.
<span class='smallblacktext'>[ Edited Wed Feb 08 2012, 06:53PM ]</span>

jber · #4 Post by **jber** » Fri Feb 10, 2012 10:04 am

Or the python tool from ASE: https://svn.fysik.dtu.dk/projects/ase/b ... eosase2.py . You need python, numpy and scipy to run it (and matplotlib to plot it):

wget https://svn.fysik.dtu.dk/projects/ase/b ... eosase2.py
$ python
>>> from eosase2 import EquationOfState
>>> volumes = [28, 31, 33, 36, 38]
>>> energies = [0.03, -0.005, -0.003, 0.04, 0.12]
>>> eos = EquationOfState(volumes, energies, eos='murnaghan')
>>> v0, e0, B = eos.fit()
>>> eos.plot()
>>> v0, e0, B
(32.203489037735132, -0.0068187976403487676, 0.16937539193434514)

jber · #5 Post by **jber** » Fri Feb 10, 2012 10:08 am

The following eos are available in the tool:

taylor
A third order Taylor series expansion about the minimum volume

murnaghan
PRB 28, 5480 (1983)

birch
Intermetallic compounds: Principles and Practice, Vol I: Principles. pages 195-210

birchmurnaghan
PRB 70, 224107

pouriertarantola
PRB 70, 224107

vinet
PRB 70, 224107

antonschmidt
Intermetallics 11, 23-32 (2003)

oldpoly
A third order polynomial fit (alternative implementation)