Abstract
The pressure effects on the electron-phonon coupling (EPC) in superconducting have been extensively studied using first-principles calculations within the rigid muffin-tin approximation. It is found that pairing electrons are mainly attributed to the Ca electrons mediated by Ca low-lying, in-plane phonon vibrations. An increase in mean square of the EPC matrix element and a decrease in Ca low-lying phonon frequency with increasing pressure are mainly responsible for the experimental observation of enhanced superconducting transition temperature. Furthermore, Mulliken population analysis suggests that the pressure-induced charge transfers from Ca to the graphite layers might mainly contribute to the softening behavior of Ca in-plane phonons.
- Received 7 August 2006
DOI:https://doi.org/10.1103/PhysRevB.74.184519
©2006 American Physical Society