From: David Vanderbilt <dhv@positron.rutgers.edu> Date: Wed, 25 Aug 1999 21:11:55 GMT (13kb)
Authors:
L. Bellaiche (Physics Department, University of Arkansas, Fayetteville),
David Vanderbilt (Center for Materials Theory, Department of Physics and Astronomy, Rutgers University)
Comments: 7 pages, two-column style with no figures. Uses REVTEX macros. Also
available at this http URL
Subj-class: Materials Science
We present an approach to the implementation of the virtual crystal approximation (VCA) for the study of properties of solid solutions in the context of density-functional methods. Our approach can easily be applied to any type of pseudopotential, and also has the advantage that it can be used to obtain estimates of the atomic forces that would arise if the real atoms were present, thus giving insight into the expected displacements in the real alloy. We have applied this VCA technique within the Vanderbilt ultrasoft-pseudopotential scheme to predict dielectric and piezoelectric properties of the Pb(Zr[0.5],Ti[0.5])O[3] solid solution in its paraelectric and ferroelectric phases, respectively. Comparison with calculations performed on ordered alloy supercells and with data on parents compounds demonstrates the adequacy of using the VCA for perovskite solid solutions. In particular, the VCA approach reproduces the anomalous Born effective charges and the large value of the piezoelectric coefficients.