Calculations and analysis of superconducting energy gap and electronic specific heat in YBa₂Cu₃O₇

The LUMO-HOMO energy gaps in YBa₂Cu₃O₇ have been calculated with density functional theory on a cluster model of unit cell of 39 atoms in a wide range of temperatures (5-300 K). Based on the energy gaps, the specific heat of electron and its coefficient have been calculated with bipolarons and thermally excited polarons model. The calculated results show that the superconducting critical temperature of YBa₂Cu₃O₇ is 93 K. The energy gaps reach minimum which is not zero at T_c; the transition points at energy gap curve are corresponding respectively for T_c, T* and T⁰. The superconducting condensed matter disappear and exhibits diamagnetism pairing pseudogap in a range of temperatures (93-120 K). The energy gap is aroused by the charge density wave of the periodic stripes phase in a range of temperature (120-200 K). When the temperature around T-T⁰, the curve of the specific heat coefficient of electron changes from increased to decreased.