A Package for calculating elastic tensors of cubic - WIEN 2k

E(v,e) = E(v 0 ,0) +v 0 [(∆ 1+ ∆ 2 ) e + ( C 11 + C 12 ) e 2 + o(e 3 )]The second type of distortion is a volume conserved distortion and lead toOrthorhombic symmetry and written as1+e 1 0 0 1+e 1 =(1+x/1-x) 1/20 1+e 2 0 1+e 2 =(1-x/1+x) 1/20 0 1and the energy for this distortion can be obtained asE(v,e) = E(v 0 ,0) +v 0 [ ( C 11 - C 12 ) x 2 + o(x 3 )]The third strain we have used is given by1 0 00 1 00 0 1+eThis strain changes C lattice parameter and keep the symmetry of thestrained lattice hexagonal and the energy for this distortion can be obtainedbyE(v,e) = E(v 0 ,0) +v 0 [(∆ 3 ) e + ( C 33 ) e 2 /2+ o(e 3 )]The fourth elastic constant, C55, is determined by means of a deformation ofthe lattice, which produces an object with low symmetry. The deformation iswritten as1 0 e0 1 0e 0 1And it leads to triclinic symmetry and the energy for this deformation can bewritten asE(v,e) = E(v 0 ,0) +v 0 [(∆ 5 ) e + (2 C 55 ) e 2 + o(e 3 )]