A non-empirical Heisenberg Hamiltonian had been proposed for conjugated 03C0 systems from ab initio calculations on ethylene, and proved to be very efficient. Its theoretical foundation from the full Hamiltonian was evident from the concept of effective Hamiltonian and the use of Quasi-Degenerate-Perturbation Theory (QDPT), as shown by Anderson. When one wants to define a Heisenberg Hamiltonian...

Transport equations for composite nucleons and deconfined quarks in quark-nuclear matter (QNM) are derived. QNM is a many-body system containing hadrons and deconfined quarks. The starting point is a microscopic quark-meson coupling (QMC) Hamiltonian with a density-dependent quark-quark interaction. An effective quark-hadron Hamiltonian containing canonical hadron and quark field operators is c...

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-depend...