README

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       PROGRAM TO DETERMINE SELF-CONSISTENT FERMI LEVEL

Energies in eV, temperature in Kelvin, DOS in states/unit cell

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j.buckeridge@ucl.ac.uk 2017
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The program calculates the self-consistent Fermi level and defect
concentrations given a set of formation energies (at VBM).

The lattice vectors of the unit cell for which the density of
states (DOS) has been calculated should be contained in a file
called 'unitcell.dat', which consists of a scaling factor,
followed by the lattice vectors in a 3x3 matrix. If this 
file is missing, but a VASP POSCAR is found, the cell parameters
will be read from the POSCAR.

The DOS should be present in a file called 'totdos.dat' which
is 2 (or 3 for spin polarised) columned, with energy and DOS
in the columns. The energy scale must be given with the VBM
(or Fermi level for a metal) set to zero (in eV). The DOS is
assumed to be in #states/cell.

The code uses a statistical mechanical approach to calculate
the concentrations of each defect in each charge state,
balanced by the free carrier concentrations from the DOS. 
Relevant equations can be found in e.g. Ashcroft and Mermin
chapter 28. The output gives a breakdown on the concentrations
in each charge state (unless the total is zero).

frozen-sc-fermi can be used to fix a particular defect 
concentration to a value of interest. You can fix the total
concentration of a defect in your original list, or one or 
more charge states (or both). You can also add extra defects
with fixed concentrations, but these must be given a 
particular charge state.

Please see the input files in the example directory, they 
should be self-explanatory.

Any questions please email me (see above).

John

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May 2017 - improved algorithms 
Feb 2018 - added warning for negative DOS values
Apr 2018 - series of bugfixes for errors occuring at low T