Relationship Between Cohesive Energy and Superconductivity in Hg-System Superconductors

Calculation of cohesive energy on Hg-system superconductors HgBa₂CuO_y(1201), HgBa₂CaCu₂O_y(1212), HgBa₂Ca₂Cu₃O_y(1223), HgBa₂Ca₃Cu₄O_y(1234), and HgBa₂Ca₄Cu₅O_y (1245) has been made. A program was developed to claculate the combinative energy between Cu-O planes and remaining parts, and between blocks in the superconductors. The result indicates that if the cell is considered as the two blocks combined together, a close relationship among the combinative energy of the two blocks, the value of T_c, and the number of the Cu-O planes in the Hg-system superconductors is established. The result gives a new way to understand the change of the value of T_c, as the number of the Cu-O planes. In contrast, the combinative energy between the Cu-O planes and the remains got from the method separating all the Cu-O planes from the cell and leaving some discrete remaining parts does not show any relationship with the value of T_c. This means that considering the cell as the two blocks in more reasonable, and the interaction between the two blocks plays an important role in superconductivity.