Ab initio molecular dynamics using density based energy functionals: application to ground state geometries of some small clusters

The ground state geometries of some small clusters have been obtained via ab initio molecular dynamical simulations by employing density based energy functionals. The approximate kinetic energy functionals that have been employed are the standard Thomas-Fermi $(T_{TF})$ along with the Weizsacker correction $T_W$ and a combination $F(N_e)T_{TF} + T_W$. It is shown that the functional involving $F(N_e)$ gives superior charge densities and bondlengths over the standard functional. Apart from dimers and trimers of Na, Mg, Al, Li, Si, equilibrium geometries for $Li_nAl, n=1,8$ and $Al_{13}$ clusters have also been reported. For all the clusters investigated, the method yields the ground state geometries with the correct symmetries with bondlengths within 5\% when compared with the corresponding results obtained via full orbital based Kohn-Sham method. The method is fast and a promising one to study the ground state geometries of large clusters.Comment: 15 pages, 3 PS figure

Thermodynamics of Na_8 and Na_{20} clusters studied with ab-initio electronic structure methods

We study the thermodynamics of Na_8 and Na_{20} clusters using multiple-histogram methods and an ab initio treatment of the valence electrons within density functional theory. We consider the influence of various electron kinetic-energy functionals and pseudopotentials on the canonical ionic specific heats. The results for all models we consider show qualitative similarities, but also significant temperature shifts from model to model of peaks and other features in the specific-heat curves. The use of phenomenological pseudopotentials shifts the melting peak substantially (~ 50--100 K) when compared to ab-initio results. It is argued that the choice of a good pseudopotential and use of better electronic kinetic-energy functionals has the potential for performing large time scale and large sized thermodynamical simulations on clusters.Comment: LaTeX file and EPS figures. 24 pages, 13 figures. Submitted to Phys. Rev.

A rearrangement of azobenzene upon interaction with an aluminum(I) monomer LAl {L = HC (CMe)(NAr)(2 ), Ar=2,6-iPr(2)C(6)H(3)

Reaction of LA1 (1) or [LA1{eta'-C-2(SiMe3)(2)}] (2) (L = HC[(CMe)-(NAr)](2), Ar = 2,6-iPr(2)C(6)H(3)) with azobenzene affords a five-membered ring compound [LA1{N(H)-o-C6H4N(Ph))}] (3). In the formation of 3 a three-membered intermediate [LA1(eta(2)-N2Ph2)] (A) is suggested by a [1 + 2] cycloaddition reaction; A is not stable and further rearranges to 3. DFT calculations on similar compounds with modified L' (L' = HCl(CMe) (NPh)](2)] show that the complexation energy of the reaction of L'Al with azobenzene to form [L'A1(eta(2)-N2Ph2)] is about -39 kcal mol(-1), and the best estimate of the energy difference between [L'A1(eta(2)-N2Ph2)] and [L'A1{N(H)-o-C6H4N(Ph))] is -76 kcal mol(-1). (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005

Polyhedral cobalt(II) and iron(II) siloxane: Synthesis and X-ray crystal structure of (RSi(OH)O-2)Co(OPMe3) (4) and (RSiO3)(2)(RSi(OH)O-2)(4)(mu(3)-OH)(2)Fe-8(THF)(4) (R = (2,6-iPr(2)C(6)H(3))N(SiMe3))

The cobalt(II) and iron(II) siloxane compounds were prepared by the reaction of lipophilic N-bonded silanetriol 1 with metal silylamides M[N(SiMe(3))(2)](2)(M = Co (2), Fe (3)) in a 1:1 and 3:4 molar ratio, respectively. A plot of 1/chi versus temperature in the range of 2-300 K indicates the paramagnetic behavior of 2 and 3. The composition and molecular structures of 2 and 3 were fully determined by IR, elemental analysis, and X-ray crystal structural analyses. Compound 2 possesses a pseudo-4-fold (S(4)) symmetry, whereas 3 reveals an inversion center. Compound 2 represents a tetracobalt(II) drum while 3 exhibits an octairon(II) cage containing siloxane ligands