Author: Daniel S. Karls (karl0100 |AT| umn DOT edu), Ilia Nikiforov (nikif002 |AT| umn DOT edu), University of Minnesota
Date: 7/23/2015

This Test Driver computes the equilibrium lattice spacing and cohesive energy of a 2D hexagonal monolayer crystal using Polak-Ribiere conjugate gradient minimization in LAMMPS. Through pipeline.stdin.tpl, the user supplies the choice of structure type, an initial guess at the equilibrium lattice spacing and the two atomic species comprising the crystal. The currently supported structures are 
1: graphene-like (e.g. h-BN or graphene) 
2: 2H structure of transition metal dichalcogenides (TMDs) (e.g. MoS2, TiSe2) 
3: 1T structure of TMDs.

For consistency between Tests created using this Test driver, the convention for inputting atomic species is:
- For structure 1, input the species in the order of the chemical formula. E.g. species 1: B, species 2: N.
- For structures 2 and 3, species 1 is the transition metal (central layer) and species 2 is the chalcogen (two outer layers).