Bipul Rakshit wrote: > Dear Michael Mehl, > I have read the two papers > http://cst-www.nrl.navy.mil/users/mehl/papers/cij453.pdf > > and > > Phys. Rev. B 47, 2493 (1993) > , > But my question is, they have given only two equation, and our unknown > quantity are 3 (C11, C12, and C44). So can we find three unknown > quantity from two equations acuratelly.
C44 is computed directly. C' = C11-C12, or maybe 1/2 (C11-C12). For a cubic crystal, B = (C11 + 2 C12)/3. That's three equations for three unknowns. C44 and C' are computed as outlined in Wang's paper, my papers, and elsewhere. The bulk modulus is obtained from B = V E''(V), and you can compute the second derivative of the energy by finding the energy at several volumes and either using one of the many equation-of-state fitting codes available, or via numerical differentiation. -- Michael J. Mehl, Naval Research Laboratory, Washington DC On Sabbatical at Duke University until 31 July 2009
