A Python tool to analyse the thermodynamics of semiconductor alloys through the Generalized Quasi-Chemical Approximation (GQCA) written by Clovis Caetano.
The GQCA approach to calculate the configurational free energy of alloys was first described in A. Sher, M. van Schilfgaarde, A. B. Chen and W. Chen, Physical Review B 36, 4279 (1987) and well explained in A. B. Chen and A. Sher, Semiconductor Alloys (Plenum Press, New York, 1995). The repository contains a Python script to perform analysis of thermodynamics of a solid solution as a statistical ensemble of independent structures. The analysis runs on the energy of the structures that describe the configurational space restricted to a specific crystallographic supercell.
As input, the scripts requires:
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number of structures
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number of species substituted with respect to pure end members
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degeneracy of each structure
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energy of the single cell
The code gqca2.py reads the file energies.dat and returns the enthalpy of mixing, configurational entropy of mixing and the Helmholtz free energy as functions of the alloy composition and temperature.
The script phase_diagram.py calls gqca2.py and calculates the binodal and spinodal points of the system for a given temperature. The code is made to automatically change the temperature, collect the phase diagram points and write them in the file phase_diagram.dat. If it doesn't work, it would be interesting to plot the free energy to understand its variation.
The script plot_phase_diagram.py just reads the file phase_diagram.dat and draws the phase diagram in a pdf file.
Note: the code was written in Python 2, but a Python 3 modification is included in a subfolder.
Thermodynamic Origin of Photoinstability in the CH3NH3Pb(I1–xBrx)3 Hybrid Halide Perovskite Alloy, Journal of Physical Chemistry Letters (2016)