21 research outputs found
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 along with the Weizsacker correction
and a combination . It is shown that the functional
involving gives superior charge densities and bondlengths over the
standard functional. Apart from dimers and trimers of Na, Mg, Al, Li, Si,
equilibrium geometries for and 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