Alan Hinchliffe

Intermolecular potentials for ammonia based on SCF–MO calculations

The results of SCF molecular orbital calculations on the ammonia dimer have been used in part to parameterize a set of atom–atom potentials. When combined with a charge distribution which reproduces the experimental dipole and quadrupole moments of the monomer, and with independent estimates of the dispersion energy, the resulting intermolecular potential yields a fair description of certain properties of the condensed phases of ammonia. Liquid ammonia is predicted to have a weakly associated character.

Ab initio calculation of the dipole polarizabilities of unsaturated hydrocarbons

Abstract 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.

Structure and properties of HSSH, H2SS, FSSF and F2SS

Abstract High quality gaussian SCF MO calculations are reported, both with and without polarization functions, for HSSH, H 2 SS, FSSF and F 2 SS. The polarization functions play an important role in the bonding of these molecules. Predicted molecular geometries of HSSH, FSSF and F 2 SS agree well with experiment when polarization functions are taken into account, and the as-yet uncharacterized isomer H 2 SS is predicted to be as stable with respect to HSSH as F 2 SS is to FSSF. One-electron properties and population analysis indices also show a marked sensitivity to inclusion of polarization functions.

Quadrupole moment calculations for some aromatic hydrocarbons

Abstract Quadrupole tensor calculations are reported for benzene, naphthalene, anthracene, phenanthrene, biphenyl (planar and twisted), pyrene, [18]-annulene and azulene. Double-zeta and STO/4G basis sets give similar ratios between naphthalene and benzene components. STO/4G calculations give out-of-plane components proportional to the number of valence electrons for all molecules except azulene.

Ab initio studies of the dipole polarizabilities of conjugated molecules: Part 5. The five-membered heterocyclics C4H4E (E = BH, AlH, CH2, SiH2, NH, PH, O and S)

Abstract We report high quality ab initio calculations of the geometries, the static dipole polarizability and the first hyperpolarizability of the electronic ground state for a series of five-membered conjugated heterocyclics C4H4E, E = BH, AlH, CH2, SiH2, NH, PH, O and S (borole, aluminocyclopentadiene, cyclopentadiene, silacyclopentadiene, pyrrole, phosphole, furan and thiophene, respectively). The geometries, fully optimized at HF/6-31G∗∗ level of theory, show good agreement with reported experimental and/or other theoretical ones. Changes induced by the heteroatom on the structural and electronic properties of these C4H4 rings are explained in terms of the heteroatom electronegativity. The sensitivity of the polarizability calculations to the variation of basis set was studied. We show that increasing the number of multiple d and p polarization functions in the 6-31 + G(nd, mp) basis set at Hartree-Fock level leads to values of the polarizability tensor components that are in good agreement with available experimental data. Electron correlation effects on the static dipole polarizability are shown to be non-negligible, when calculated at the MP2/6-31 + G(d,p) level of theory for borole, cyclopentadiene, pyrrole, furan and thiophene. We find that the calculated average dipole polarizability of these molecules is linearly related to the bond distance “a” C-E of the C4H4E ring with a correlation coefficient of r2 = 0.98, by α ave 10 −40 CV −1 m 2 = 1.523 + 4.973a a 0 with phosphole being an exception; this compound shows an enhanced and anomalous polarizability with respect to the rest of the series. In addition, we show that these polarizabilities can be used as an aromaticity scale for explaining the known aromaticity in compounds such thiophene, pyrrole and furan. We also give the first-ever high quality calculation at the HF/6-31 + G(3d,3p) level of theory for the first hyperpolarizability tensors of these molecules.

Ab initio calculations of electric field gradient for the B…HCl dimers: B=CO, HCN, H2O, H2S, C2H2, C2H4, NH3, PH3 and CH3CN

Abstract Ab initio calculations of electric field gradient have been performed for the H-bonded directs B…HCl, where B=CO, HCN, H 2 O, H 2 S, C 2 H 2 , C 2 H 4 , NH 3 , PH 3 and CH 3 CN, with an STO/4-31G basis set. The influence of geometry relaxation on the properties is investigated. The nuclear quadrupole coupling constant χ( 35 Cl) has been evaluated for each dimer and its change from the free HCI subunit value (χ 0 ) upon direct formation analyzed. Total atomic charges, dipole and quadrupole moments were also calculated. Comparison with a recent experimental work is given.

The polarisability of LiCl as a function of bond distance

Abstract We report a near-Hartree—Fock-limit calculation of the variation of the polarisability of LiCl with bond distance over the range 2 a 0 to 20 a 0 . The results, which are of interest in the IBC model of light scattering, are broadly similar to corresponding calculations on Ne 2 and He 2 .

Structure and properties of FCO, FOO, ClCO and ClOO

Abstract High quality SCF-MO calculations for the radicals FCO, FOO, ClCO and ClOO including geometry optimization are presented. One-electron properties and population indices are reported and compared both with experiment where appropriate and amongst themselves. 35 Cl-quadrupole coupling constants agree well with the experimental data and the agreement between calculated and observed ESR hfcc is discussed.

Ab initio studies of the dipole polarizabilities of conjugated molecules: Part 2. Monocyclic azines

We report high quality ab initio calculations of the dipole polarizability and first hyperpolarizability of the following single monoeyclic azines: pyridine, pyridazine, pyrimidine, pyrazine, s-triazine and s-tetrazine. A study of the sensitivity of such calculated properties to the variation of basis set shows that increasing the number of multiple d and p diffuse functions in the 6-31 + G(nd, mp) basis set at Hartree-Fock level gives values of the polarizability tensor components that are comparable with the experimental ones, and consistent values of hyperpolarizability tensor components. We have also found that correlation effects are negligible, provided that such calculations are performed at the SCF level with very extended basis sets. We show that standard sp basis sets need to be extended in the sp space, to have extra diffuse functions added and also to include suitable d and p gaussian primitives in order to be useful for the calculation of response functions. We find that the average dipole polarizability (αave) is related to the number of nitrogen atoms N in the ring by αave/10−40(CV−1 m2) = 10.90–0.90N We also find that the calculated average and anisotropy polarizability components are both linearly related to the sum of the HOMO and LUMO orbital energies. We also give the first ever high-quality calculation of the hyperpolarizability tensors for these molecules. Electric dipole and quadrupole moments agree well with experiment, as do the asymmetry parameter and the nitrogen quadrupole coupling constants.

Ab initio study of the hydrogen-bonded complexes NH3 ⋯ HX, PH3 ⋯ HX and NH3 ⋯ (HX)2 where X F, Cl

Abstract Large-scale Gaussian orbital SCF—MO calculations are presented for the title molecules. Calculated equilibrium geometries, hydrogen-bond dissociation energies and one-electron properties are given to supplement available experimental data. Changes of electron distribution on complex formation are discussed in terms of Mulliken population analysis indices.