Finite-field SCF Research Articles

Modeling hyperpolarizabilities of some TICT molecules and their analogs

Ground-state hyperpolarizabilities of a prototypical twisted intramolecular charge transfer (TICT) molecule (DMABN) and its analogues have been calculated by the finite-field SCF method at the CNDO/S level of approximation. The ground-state geometry of each molecule has been optimized by the MNDO metbod. Excited-state hyperpolarizabilities have been calculated by invoking the finite-field SCF single excitation CI method at the CNDO/S level of approximation. The study focuses attention on the possibly important role played by the TICT state in generating large quadratic polarizability in some of these molecules

On the Electric Multipole Moments of Carbon Monoxide

Abstract The electric dipole, quadrupole, octopole and hexadecapole moment of carbon monoxide has been obtained from finite-field SCF and Moeller-Plesset perturbation theory calculations. The resulting values for the octopole and hexadecapole moments of CO(X1 Σ+ ) are 3.59 eao 3 and - 9.01 eao 4 respectively

Finite-field SCF calculations of the dipole polarisabilities of heavy atoms using relativistic effective potentials

The static dipole polarisabilities of Xe, Lu, Hg+, Hg, Tl and At have been determined from finite-field SCF calculations within a valence-electron relativistic effective potential formalism. The effect of the self-consistent inclusion of spin-orbit coupling on the calculated polarisabilities have been investigated by comparing j-averaged (L, Lambda ) results with j-dependent (J, Omega ) calculations. The atoms selected provide a range of closed-shell, particle and hole states for comparative study. The results suggest that self-consistent inclusion of spin-orbit coupling is far more important for the particle states than for the hole states. In the case of Xe, results are presented from calculations using relativistic effective potentials based on both Hamiltonian-consistent and shape-consistent pseudo-orbitals. The shape-consistent approach is found to produce polarisabilities in better agreement with previously determined all-electron Hartree-Fock values. In addition, for Hg the shape-consistent approach yields a polarisability in excellent agreement with all-electron numerical Dirac-Fock calculations.

Reliable static electric dipole polarizabilities for heavy elements

The static electric dipole polarizabilities for Rb and Cs are obtained from finite-field SCF and CI calculations using relativistic effective potentials developed by Christiansen et al. Results agree with the experimental values or Molof et al. to within ≈ 5xxx. By contrast, calculations using Phillips-Kleinman type potentials for Cs were seriously in error

An SCF calculation of the pair polarizability of argon

The finite field SCF method has been used to calculate the pair polarizability of argon; a gaussian basis set was employed. The computed anisotropy and trace are compared with models obtained from Raman spectroscopy, and also with results from perturbation theory. Analytic fits to the anisotropy function are examined. Long range convergence to DID values is obtained for both the trace and anisotropy. However the trace exceeds the DID value in a range of separation between the well and 13 a 0. Values for the second Kerr and dielectric virial coefficients are calculated. An accurate form of the anisotropy is proposed.

Ab initio calculation of the dipole polarizabilities of unsaturated hydrocarbons

Finite-field SCF MO calculations of polarizability are reported for ethene, benzene and naphthalene using three good gaussian basis sets Double-zeta wavefunctions yield values of α LL and α MM in agreement with experiment but the calculated α NN is half the experimental value. Polarization functions when present preferentially improve α NN . ( L,M) and N refer to the molecular long, medium and normal axes, respectively.) STO-4G results are given for benzene, naphthalene, azulene, anthracene and phenanthrene, and the agreement with the experiment is reasonable after scaling the calculated α LL and α MM by a constant factor. The calculated α MM are an order of magnitude too low.

Comparison of multipole moment expansions by direct summation or finite-field SCF methods with full electrostatic interaction energies: Application to CO and N 2

In calculations of the electrostatic interactions of molecules with external potentials the multipole expansion is frequently employed. In this paper the usefulness and validity of this method are investigated. Two types of potential, that due to a point charge and that near the (100) surface of a NaCl crystal have been considered, and numerical results are presented for CO and N 2. Multipole expansions up to the hexadecapole level have been calculated both by the summation of moment contributions and by a finite-field SCF approach. Problems in applying the expansion technique are discussed. An alternative method for calculating interactions with potentials of arbitrary functional form is proposed. A possible explanation of the differences in physisorption of CO and N 2 is advanced. A comparison of electrostatic potential curves for N 2 using an extended basis set with those published for a minimal basis set are given and important differences are examined.

Carbon monoxide bond length, force constant and infrared intensity variations in strong electric fields: Valence-shell calculations, with applications to properties of adsorbed and complexed CO

The approximate finite-field SCF method with valence orbital basis set used earlier (N. S. Hush and M. L. Williams, Chem. Phys. Lett. 5, 507, 1970; 6, 163, 1970) to calculate molecular polarizability tensor components is extended to examine the effects of strong electric fields on equilibrium nuclear configurations, vibration frequencies and vibrational transition intensities. Results for the carbon monoxide molecule in axial fields are reported and analyzed in this paper. These are applied to interpretation of infrared absorption measurements for weakly adsorbed CO, and infrared and CO bond-length measurements for carbonyl complexes.