Experimental magnetic form factors in Co3V2O8: A combined study of ab initio calculations, magnetic Compton scattering and polarized neutron diffraction

We present a combination of ab initio calculations, magnetic Compton scattering and polarized neutron experiments, which elucidate the density distribution of unpaired electrons in the kagome staircase system Co3V2O8. Ab initio wave functions were used to calculate the spin densities in real and momentum space, which show good agreement with the respective experiments. It has been found that the spin polarized orbitals are equally distributed between the t2g and the eg levels for the spine (s) Co ions, while the eg orbitals of the cross-tie (c) Co ions only represent 30% of the atomic spin density. Furthermore, the results reveal that the magnetic moments of the cross-tie Co ions, which are significantly smaller than those of the spine Co ions in the zero-field ferromagnetic structure, do not saturate by applying an external magnetic field of 2 T along the easy axis a, but that the increasing bulk magnetization originates from induced magnetic moments on the O and V sites. The refined individual magnetic moments are mu(Co_c)=1.54(4) mu_B, mu(Co_s)=2.87(3) mu_B, mu(V)=0.41(4) mu_B, mu(O1)=0.05(5) mu_B, mu(O2)=0.35(5) mu_B, and; mu(O3)=0.36(5) mu_B combining to the same macroscopic magnetization value, which was previously only attributed to the Co ions

MODELLING OF OPTICAL SPECTRA OF MATRIX-ISOLATED SOLVER-HOLMIUM SPECIES

Author Institution: Department of Chemistry, Moscow State University; Department of Chemistry, Max-Plank Institut fuer StrahlenchemieAb initio pseudopotential calculations have been carried out for the series of holmiumcontaining species in order to provide an assignment of the bands observed in UV-visible spectra of matrix isolation experiments. The formation of the pure holmium as well as the mixed holmium-silver clusters is expected under the experimental conditions, and the following species have been considered theoretically: $Ho_{2}, Ho_{3}, Ag_{2}, Ag_{3}, AgHo, Ag_{2}Ho, AgHo_{2}$. The configuration interaction calculations with single and double excitations have been applied to estimate the transition energies and transition moments. The Stevens-Basch-Krauss pseudopotential and the corresponding basis set have been used for silver. Two sets for the holmium pseudopotential and basis function parameters borrowed from the Stuttgart group tables have been employed. Namely, the search of the equilibrium geometry configurations of the holmium-containing clusters has been performed at the Hartree-Fock level with the $Q=11$ pseudopotential, describing the holmium atom in the $4f^{10}6s^{2}5d^{1}$ electronic state, and the calculations of the energy levels for the established geometries have been carried out with the $Q=10$ pseudopotential corresponding to the true $4f^{11}6s^{2}$ atomic configuration. A single empirical correction parameter has been introduced for the predicted band positions in the electronic spectra when taking into account the firmly established results for the matrix-isolated species $Ag, Ho, Ag_{2}, Ag_{3}$. With such a correction, the computed wavelengths for the strong bands in the spectra of $Ho_{2}$ (500 nm) and AgHo (432 nm) are in excellent agreement with the tentative experimental assignments 498/504 nm for $Ho_{2}$ and 430 nm for AgHo. No theoretical support has been provided for the formation of metal trimers in the experiments

SIMULATIONS OF ARGON-INDUCED VIBRATIONAL RED SHIFTS IN HF

1. J.M. Hutson, J. Chem. Phys. 96, 6752 (1992) 2. F.M. Tao, and W. Klemperer, J. Chem. Phys. 101, 1129 (1994) 3. S. Liu, Z. Bacic, J.W. Moskowitz, and K.E. Schmidt, J. Chem. Phys. 100, 7166 (1994); 101, 6359 (1994); 101,Author Institution: Moscow State University, Moscow, 119899 GSP, RUSSIA.Molecular dynamics calculations have been carried out in order to simulate vibrational red shifts for the HF molecule coupled to argon clusters $Ar_{n} (n = 1-62)$. The interaction potential for each Ar-H-F trimer has been constructed following the ideas of the diatomics-in-molecules approach. If both neutral and ionic states of hydrogen and fluorine are taken into account, the triatomic PES incorporating non-additive contributions is consistent with the surfaces described $previously^{1,2}$. Combined with the conventional Ar-Ar interaction potentials, molecular dynamics treatment leads to correct vibrational red shifts for HF induced by argon $clusters^{3}$. These calculations manifest directly the importance of many-body effects for an adequate prediction of properties of matrix-isolated molecules

MOLECULAR DYNAMICS SIMULATION OF THE 3Πg^{3}\Pi_{g} (ION-PAIR) →3Πu\rightarrow ^{3}\Pi_{u} (VALENCE) RED-SHIFTED TRANSITIONS OF Cl2Cl_{2} IN NEON MATRICES

$^{a}$ B.L. Grigorenko, A.V. Nemukhin, A.A. Buchachenko, N.F. Stepanov, and S. Ya. Umanskii, J.Chem.Phys. 106, 4575 (1997). $^{b}$ B.L. Grigorenko, A.V. Nemukhin, and V.A. Apkarian, Chem.Phys. 219, 161 (1997).Author Institution: Department of Chemistry, Moscow State UniversityThe features of the emission bands corresponding to the transition from the ion-pair $^{3}\Pi_{g}$ state to the valence $^{3}\Pi_{u}$ state of $Cl_{2}$ in neon matrices have been modelled by the molecular dynamics simulations with the diatomics-in-molecules (DIM) interaction $potentials^{a,b}$. The experimental potential curves of $Cl_{2}$ in the gas phase have been employed for initial numerical calculations of the $^{3}\Pi_{g}(v^{\prime})\to^{3}\Pi_{u}(v^{\prime \prime})$ band positions and the corresponding Franck-Condon factors. The matrix-perturbed potential curves of the trapped $Cl_{2}$ molecule have been evaluated by the direct calculation of the corresponding cuts through the $Cl_{2}@Ne_{n}$ multi-dimentional potential energy surface constructed with the DIM techniques. The parameters of the model have been verified at the preliminary stage on the three-atomic van der Waals complex $Ne\ldots Cl_{2}$. The results of simulations show a remarkable coincidence with the experimental findings of Guertler, Kunz and Le Calve [J.Chem.Phys. 91 (1989) 6020], namely, the matrix environment causes the quantitatively reproduced red shifts in the$(0, v^{\prime \prime})$ band positions as well as the noticeable changes in band intensities

AB INITIO PREDICTIONS OF IR SPECTRA FOR THE GRIGNARD REAGENTS.

1. Y. Imuzu, and K.J. Klabunde, Inorgan, Chem, 23, 3602 (1984) 2. B.S. Ault. JACS 102, 3480 (1980) 3. P.J. Jasien, and C.E. Dykstra, JACS 105, 2089 (1983); 107, 1891 (1985)Author Institution: Moscow State University, Moscow. 119899 GSP, RUSSIA.; "PRI/Dyn Corp., National Cancer Institute-Frederick Cancer Research and Development Center", Frederick, MD 21702, USA.Ab initio calculations have been carried out to characterize Grignard reagents $CH_{3}MgX$ and $CH_{3}MgMgX (X=F, Cl, Br)$. Positions and intensities of IR spectra have been predicted for these species as well as for other possible products of matrix $reactions^{1}$ of magnesium with $CH_{3}X$ at the uniform theoretical level $(SCF/6-31G^{\ast})$. Relative stabilities have been discussed on the basis of the MP2 theory. For the fluorine species unusual complexes of Grignard reagents with magnesium have been studied with the help of the density functional approach. Comparison with previous $findings^{2,3}$ has been discussed as well as with preliminary experimental results of cryogenic syntheses of such substances