2022-05-19T06:37:46Zhttps://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, KojiYamaki, DaisukeCopyright (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.We 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.American Institute of Physics2004-09-01engjournal articlehttp://hdl.handle.net/2237/8738https://nagoya.repo.nii.ac.jp/records/7064http://dx.doi.org/10.1063/1.1772354JOURNAL OF CHEMICAL PHYSICS121939643972https://nagoya.repo.nii.ac.jp/record/7064/files/ChemPhys_121-3964.pdfapplication/pdf147.0 kB2018-02-19