Simulation techniques in parametric Hamiltonians

Using simulation techniques, a general definition of parametric Hamiltonians (H_pa), is presented. The minimal distance between a parametric and the exact Hamiltonian (H_exa) is defined in terms of the sum of the least distance between the corresponding energy functional components. A reference electronic energy functional for simulation of H_exa is proposed based on a CI energy functional. General properties of parametric Hamiltonians are analyzed considering reduction of the number of particles, integrals, and basis set, elimination of orthogonal transformations, and correlation and total energy functionals. Parametric Hamiltonians based on simulation of binding energy functionals and a simple parametrization scheme are proposed. Some preliminary tests have been performed with the parametrization of a characterized H_pa and calculations of organic (CH₄, C₂H₂, C₂H₄, and C₂H₆) and transition metal (Ni₂ and Ni₅) systems.