Computation of Materials Properties from First Principles
S. G. Louie and M. L. Cohen, University of California, Berkeley, and Lawrence Berkeley National Laboratory
Research Objectives
Determination and prediction of the structure of materials using quantum theories.
Computational Approach
Materials properties are computed using (1) the density functional formalism by solving a set of self-consistent Schrdinger-like equations and (2) many-body perturbation theory by solving the one- and two-particle Green's functions. Computations involve extensive determination and manipulation of the eigenvalues and eigenvectors of large matrices with dimensions up to several hundred thousand on the Cray C90 and T3E.
Accomplishments
First-principles calculations have been performed on a number of materials systems. The C36 fullerene was predicted to have several interesting electronic properties, some of which have now been observed experimentally. Nuclear magnetic resonance (NMR) chemical shift calculations of several materials have been performed. A new theory was developed and applied to the ab initio study of the optical properties for solids and clusters. Studies have been performed pertaining to the periodic trends of hard materials.
Significance
C36 is a smaller cousin of the famous C60 "buckyball." We predicted that C36 could be synthesized, and that it should be very interesting. Notably, it has a larger electron-phonon interaction than C60 does, which suggests that it may be a higher-temperature superconductor. If this is the case, C36 could have a wide range of practical applications. Experimentalists with whom we are collaborating have since synthesized and purified C36 and are in the process of characterizing it.
Calculating the optical properties of solids from first principles has been a long-sought goal of physicists. For the first time, our method enables such calculations for insulators and semiconductors. This approach not only provides quantitative understanding, but also the means of predicting the optical responses of new materials.
A proposed crystal structure for C36 solid. The shaded region corresponds to electron density, indicating strong covalent bonds between C36 molecules.
Publications
M. Rohlfing and S. G. Louie, "Electron-hole excitations in semiconductors and insulators," Physical Review Letters 81 (11), 2312-2315 (1998).
M. Cote, J. C. Grossman, M. L. Cohen, and S. G. Louie, "Electron-phonon interactions in solid C36," Physical Review Letters 81 (3), 697-700 (1998).
Y.-G. Yoon; B. G. Pfrommer, F. Mauri, and S. G. Louie, "NMR chemical shifts in hard carbon nitride compounds," Physical Review Letters 80 (15), 3388-91 (1998).