FIRST-PRINCIPLES CALCULATION OF THE TRANSITION-TEMPERATURE T-C FOR HGBA2CUO4-TEMPERATURE SUPERCONDUCTORS VIA DIPOLON THEORY(DELTA HIGH)

First numerical evaluations of T-c for oxygenated and argon-reduced si ngle-layered HgBa2CuO4+delta superconductors have been presented. Our calculations are based on the dipolon theory and are found to provide an explanation for the occurrence of superconductivity in single-layer ed high-T-c superconductors. Relevant expressions useful for the evalu ation of T-c have been given. Since the polarizabilities of the ions a re not known exactly for the present systems we have performed calcula tions making use of Pauling's as well as Tessman, Kahn, and Shockley's polarizabilities in order to estimate the uncertainties in the calcul ated values of T-c associated with uncertainties in the polarizabiliti es. The effective charges on the ions required for the evaluation of d ipoles and dipolon frequencies have been obtained by means of the bond -valence sums. Without fitting with any parameters, our calculations y ield T-c values equal to 80+/-21 K for the oxygenated and 50+/-27 K fo r the argon-reduced HgBa2CuO4+delta, superconductors, in agreement wit h the corresponding experimental values 95 and 59 K. The uncertainties in the calculated values of T-c arise because of the uncertainties in various physical parameters (including polarizabilities) used and due to errors involved in the calculations. The present results are consi stent with the observed electronic Raman-scattering intensities which show anomalously broad peaks extended up to several electron volts in cuprate high-T-c superconductors. Our calculated dipolon density of st ates predict four optical absorption peaks at about 77 cm(-1), 195 cm( -1), 1.6 eV, and 2.5 eV.