Study of the Quasi-Canonical Localized Orbital (QCLO) method based on protein structures

Abstract

We have developed a density functional(DF) program, ProteinDF for all-electron calculation on proteins. In order to overcome difficulties of a convergence problem in large-scale molecules, we already proposed a new localized orbital (LO), which named Quasi-Canonical LO (QCLO). The previous convergence process using QCLOs paid attention to the primary structure and adopted linear elongation by the arithmetric series. In this study, a new convergence process is proposed by taking the secondary structure into consideration such as hydrogen bonds and salt bridges, and those linkages are calculated in pairs here. The effectiveness of the new process was discussed by comparing with the values of the original method, i.e. the total energy, convergence history and difference of Mulliken populations between initial and converged states. As a result, we proved the new convergence processes gave significantly better initial guess than previous one. This method could be useful for safe and automatic all-electron DF calculations on very large-scale proteins.