2022-05-16T06:25:22Zhttps://nagoya.repo.nii.ac.jp/oaioai:nagoya.repo.nii.ac.jp:000070642021-03-01T12:28:46ZSimple minimum principle to derive a quantum-mechanical/molecular-mechanical methodYasuda, Koji19051Yamaki, Daisuke19052We propose a minimum principle to derive a QM/MM (quantum-mechanical/molecular-mechanical) method from the first principle. We approximate the Hamiltonian of a spectator substituent as the structure-dependent effective Hamiltonian in a least-squares sense. This effective Hamiltonian is expanded with the orthogonal operator set called the normal-ordered product. We determine the structure-dependent energy that corresponds to the classical MM energy and the extra one-electron potential that takes account of the interface effects. This QM/MM method is free from the double-counting problem and the artificial truncation of the localized molecular orbitals. As a numerical example we determine the one-electron effective Hamiltonian of the methyl group. This effective Hamiltonian is applied to the ethane and CH3CH2X molecules (X=CH_3, NH_2 , OH, F, COOH, NH^＋_3 , OH^＋_2 , and COO^-). It reproduced the relative energies, potential energy curves, and the Mulliken populations of the all-electron calculations fairly well.journal articleAmerican Institute of Physics2004-09-01application/pdfJOURNAL OF CHEMICAL PHYSICS912139643972http://hdl.handle.net/2237/8738https://nagoya.repo.nii.ac.jp/record/7064/files/ChemPhys_121-3964.pdfenghttp://dx.doi.org/10.1063/1.1772354Copyright (2004) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.