No abstract

A new methodology of binding energy calculation with respect to different spin arrangements for a multiatomic electron system is developed from the first principle in the frame of the exchange perturbation theory (EPT). We developed EPT formalism in the general form of the Rayleigh-Srchödinger expansion with a symmetric Hamiltonian, taking into account an exchange and nonadditive contributions of a superexchange interaction. The expressions of all corrections to the energy and wave function were reduced to the nonsymmetric Hamiltonian form. The EPT method is extended for the case of degeneracy in the total spin of a system. As an example of the application of the developed EPT formalism for the degeneracy case, spin arrangements were considered for the key Mn -O-Mn ( Mn : Mn 3+ or Mn 4+ ) fragments in manganites. In Mn -O-Mn for La 1/3 Ca 2/3 MnO 3 are in good agreement the obtained estimations of Heisenberg parameter and binding energy with the available experimental data.

No abstract

We present the formalism of Time-dependent Exchange Perturbation Theory (TDEPT) built to all orders of perturbation, for the arbitrary time dependency of perturbation. The theory takes into account the rearrangement of electrons among centres. We show how the formalism can be reduced to the standard form of invariant perturbation theory by "switching off" the re-arrangement of electrons among centres. The elements of the scattering S-matrix and transitions T-matrix and the formula for the electron scattering differential cross section are derived. The application of the theory to scattering and collision problems is discussed. As an example, we apply the theory to proton scattering on a Lithium atom, calculating the differential and total cross-sections.

No abstract