1ST-PRINCIPLES INVESTIGATION OF THE SUPERCONDUCTING PROPERTIES OF TL2BA2CACU2O-DELTA AND THE SPIN INSTABILITY OF CR USING A NEW APPROACH OF CONFIGURATION-INTERACTION OF BAND-STRUCTURE WAVE-FUNCTIONS

Antiferromagnetism and superconductivity result from fluctuations of electrons in states near the Fermi energy driven by the Coulomb interaction. We investigate the superconducting instability for Tl2Ba2CaCu2O8 for the perfect and distorted tetragonal crystal structure and test this method by studying the antiferromagnetic state of Cr utilizing a new ab initio technique. We numerically diagonalize a Hamiltonian of the Coulomb interaction expressed in terms of basis states that consist of Slater determinants of first-principles band-structure eigenfunctions over a mesh of points in k space. The response functions are then computed for spin-density waves, charge-density waves, and superconductivity to obtain the characteristic of the ground state. Results for Cr agree well with previous calculations. For 2:2:1:2 we find superconductivity is most favorable only for the recently reported distorted structure, which causes the Tl s band to lie above the Fermi energy. © 1990 The American Physical Society.