STRUCTURAL-PROPERTIES OF STAGE-2 ALKALI-METAL GRAPHITE-INTERCALATION
COMPOUNDS - A MOLECULAR-DYNAMICS STUDY
Cagin-T, Sen-S, Seong-H and Mahanti-SD,
Molecular Simulation 10, 41(1993)
ABSTRACT
An extensive study on low temperature solid and high temperature liquid
phases of stage 2 alkali-metal graphite intercalation compounds (GICs), as
examples of two dimensional screened Coulomb (repulsive) systems on
strongly corrugation modulated substrates, is presented using constant
energy and constant temperature (Nose) Molecular Dynamics (MD) simulations.
We present pair correlation functions, static structure factors and
snapshots of microscopic structures in the liquid phase, in the freezing
region and in the solid phase. Average energy, diffusion constant and the
number of disclinations are monitored as a function of temperature to track
down the transition (freezing) region. We also find that the number density
of the topological defects (such as dislocations and disclinations)
decreases rapidly at the freezing transition. In the solid phase of RbC24
we find small triangular domains of (square-root 7 x square-root 7) Rb
structure with well defined domain walls consisting of (2 x 2) and (2 x 3 x
square-root 7) elemental plaquettes of Rb. These nanostructures provide a
clear picture of the discommensurations (domain walls) and a consistent
understanding of the X-ray diffraction measurements. Our simulation studies
suggest a Periodic Domain Wall model to describe the low temperature solid
phase structure of the alkali metal GIC's. This model explains the dominant
features of the experimental X-ray structure factor.