Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCF?MO?LC(LCGO) Methode. II. Das Benzol (C6H6)

The C₆H₆ has been investigated ab initio for the equilibrium distance of the centers, taking into account all 42 electrons, using the Allgemeines Programmsystem/SCF ? MO ? LC (LCGO ) Methode. A total energy of ?227.27 a.u. and an ionization energy of 8.5 eV were found. Further one of the π orbitals was more strongly binding than some of the σ orbitals.     

Direct evaluation of one-electron properties in coupled cluster methods

Summary An analysis of a method for approximate calculations of expectation values for one-electron operators from available coupled cluster amplitudes is presented and illustrated numerically for the polarizability of the Be atom. The one-particle density matrix resulting from the present approach is accurate through the fourth order in the electron correlation perturbation. It has been found that, in order to obtain quantitative agreement between the energy derivative results and the approximate expectation value formalism, the third orderT ₁ T ₂⁽⁰⁾ wave function term must be included into the calculation of the one-particle density matrix. The present method is also considered as a promising tool for calculations of higher-order atomic and molecular properties from high level correlated wave functions.     

SCF MO LCGO studies on the hydration of ions: The system Li+·2H2O

The energy of the dihydrated lithium cation Li⁺·2H₂O is studied in several different points within the SCF MO LCAO framework, using a gaussian basis set to approximate the wavefunction. The computed binding energies (hydration energies) and bond distances are compared to the values found for the monohydrate. The results are discussed in view of ion-solvent interaction, and especially of the effect of ions on adjacent hydrogen bonds, in aqueous solutions.It is a pleasure to thank our technical staff for the careful preparation of the input for the programs and for its enthusiastic and skilful assistance in running the computer.     

Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCF?MO?LC(LCGO) Methode. V. Bindungsbeteiligung der Inneren Elektronen des C-Atoms

Using the results of ab initio calculations, by comparison of the “1s orbital energies” of the C atom in the compounds C₆H₆, C₅H, C₃H₆ (cyclopropane), C₂H₄ as well as at the C atom itself the bond electrons were found to have a significant influence on the inner electrons. The reason for this is pointed out and an explanation is given. The connection between the bonding and this “1s orbital energy” change as well as the importance of this result for quantum-chemical “models” is discussed.     

Finite-field many-body perturbation theory. VI. Multipole polarizabilities of beryllium. A comparative study

A high-resolution ESCA N1s spectrum from free p-aminobenzonitrile molecules is presented. The spectrum is very different from the corresponding spectrum from a solid sample. It shows one uncommonly intense shape-up line from the N1s ionization in the nitrile group, while ionization in the NH₂ group does not give rise to any such anomalous shake-up features. The spectrum is theoretically analyzed by means of a large-scale ab initio calculation by the CAS SCF method, in which a full π-orbital active space was employed for the ground and N1s ionic states. The calculations strongly underline the role of multiple excitations in the charge transfer following N1s(CN) ionization, as well as the importance of separate self-consistent treatment of all states involved. In particular, it is shown that an unsuitable choice of orbitals can lead to an apparent “shake-down”.     

Symmetric group approach to relativistic CI. I. General formalism

General formulas for matrix elements of spin-dependent operators in a basis of spin-adapted antisymmetrized products of orthonormal orbitals are derived. The resulting formalism may be applied to construction of the Hamiltonian matrices both for Pauli and for projected no-pair relativistic configuration interaction methods. From a formal point of view, it is a generalization of the symmetric group approach to the CI method for the case of spin-dependent Hamiltonians. © 1997 John Wiley & Sons, Inc.