We describe improved algorithms for carrying out pseudospectral Hartree–Fock calculations; these algorithms are applicable to other ab initio electronic structure methodologies as well. Absolute energies agree with conventional basis set codes to within 0.25 kcal/mol, and relative energies agree to better than 0.1 kcal/mol for a wide variety of test molecules. Accelerations of CPU times of as large as a factor of 6.5 are obtained as compared to GAUSSIAN 92, with the actual timing advantage increasing for larger basis sets and larger molecules. The method is shown to be highly reliable and capable of handling extended basis sets.

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From ab initio calculations on various clusters representing the La2-xSrxCu(1)O(4) and Y(1)Ba(2)Cu(3)O(7) classes of high-temperature superconductors, it is shown that (i) all copper sites have a Cu(II)(d(9))oxidation state with one unpaired spin that is coupled antiferromagnetically to the spins of adjacent Cu(II) sites; (ii) oxidation beyond the cupric (Cu(II)) state leads not to Cu(III) but rather to oxidized oxygen atoms, with an oxygen ppi hole bridging two Cu(II) sites; (iii) the oxygen ppihole at these oxidized sites is ferromagnetically coupled to the adjacent Cu(II)d electrons despite the fact that this is opposed by the direct dd exchange; and (iv) the hopping of these oxygen ppi holes (in CuO sheets or chains) from site to site is responsible for the conductivity in these systems (N-electron band structures are reported for the migration of these localized charges).

We present a new algorithm for performing ab initio solution phase geometry optimizations. The procedure is based on the self consistent-reaction-field method developed in our laboratory which combines electronic structure calculations with a finite element formulation of the continuum electrostatics problem. A gradient for the total solution phase free energy is obtained by combining different contributions from the gradient of the classical polarization free energy and the derivatives of the quantum mechanical energy. The method used in obtaining the classical gradient is based on exact linear algebra relations and a Green function formalism due to Handy and Schaefer. Both the classical and quantum mechanical gradients are validated by comparison with energy finite differences. The result of applications to a number of small organic compounds are discussed. Comparisons between the predicted location and depth of the various solution phase minima of the Ramachandran map for the alanine dipeptide and those reported by Gould et al. are also presented.

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