First principles molecular dynamics simulation of carbon at high pressures and temperatures
Grumbach, Matthew Philip
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https://hdl.handle.net/2142/18873
Description
Title
First principles molecular dynamics simulation of carbon at high pressures and temperatures
Author(s)
Grumbach, Matthew Philip
Issue Date
1993
Doctoral Committee Chair(s)
Martin, Richard M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
molecular dynamics
carbon simulation
high pressure
high temperature
density functional theory
Language
en
Abstract
"The unified method for molecular dynamics and density functional theory introduced by
Car and Parrinello has made possible accurate thermodynamic calculations on a wide variety
of materials. The key to this method is a highly efficient means for computing the electron
density as a function of the positions of the nuclei, which then leads to accurate forces on
the nuclei. In this thesis we extend the original method based on finite temperature density
functional theory and we present an extensive study of the phases of carbon at high temperatures
and pressures. Our extension provides a general method to treat electronic states at
finite temperature or in non-equilibrium excited states, alleviates convergence problems that
arise when iterative methods are applied to metals, and provides a framework that allows
fractional occupation numbers to vary dynamically during the simulation of metallic systems.
The method is illustrated by calculations on crystalline metallic carbon and simulations of
liquid silicon. Very little is known about the phase diagram of carbon at high pressures and
temperatures since these conditions are currently outside the reach of experiment. We have
performed a series of first principles molecular dynamics simulations which elucidate three
aspects of the phase diagram: 1) the melting of the simple cubic phase at """"35 Mbar; 2)
evidence for a structural change in the liquid in the range of 3-8 Mbar; and 3) the melting
of the BC-8 phase at """"20 Mbar. We combine the results of these three investigations to
construct a proposed phase diagram for carbon at high temperatures and pressures."
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