Orbital-Free Molecular Dynamics Simulations of Melting in Na8 and Na20: Melting in Steps

Details Orbital-Free Molecular Dynamics Simulations of Melting in Na8 and Na20: Melting in Steps Orbital-Free Molecular Dynamics Simulations of Melting in Na8 and Na20: Melting in Steps

1998-09-14

arxiv.org/abs/physics/9809019v2

J. Chem. Phys. 111 (1999) 6026

Physics

Atomic and Molecular Clusters

Revised version, accepted for publication in J. Chem. Phys. The changes include longer simulations for the Na20 microcluster,

Scientific paper

10.1063/1.479899

The melting-like transitions of Na8 and Na20 are investigated by ab initio constant energy molecular dynamics simulations, using a variant of the Car-Parrinello method which employs an explicit electronic kinetic energy functional of the density, thus avoiding the use of one-particle orbitals. Several melting indicators are evaluated in order to determine the nature of the various transitions, and compared with other simulations. Both Na8 and Na20 melt over a wide temperature range. For Na8, a transition is observed to begin at approx. 110 K, between a rigid phase and a phase involving isomerizations between the different permutational isomers of the ground state structure. The ``liquid'' phase is completely established at approx. 220 K. For Na20, two transitions are observed: the first, at approx. 110 K, is associated with isomerization transitions between those permutational isomers of the ground state structure which are obtained by interchanging the positions of the surface-like atoms; the second, at approx. 160 K, involves a structural transition from the ground state isomer to a new set of isomers with the surface molten. The cluster is completely ``liquid'' at approx. 220 K.

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