Ab initio quantum molecular dynamics method based on the restricted-path integral: Application to electron plasma and an alkali metal
AdvisorDeymier, Pierre A.
Chambers, Robert H.
MetadataShow full item record
PublisherThe University of Arizona.
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AbstractWe develop a new Quantum Molecular Dynamics simulation method. The method is based on the discretized path integral representaion of quantum mechanics. In this representation, a quantum particle is isomorphic to a closed polymer chain. The problem of the indistinguishability between quantum particles is tackled with a non-local exchange potential. When the exact density matrix of the quantum particles is used, the exchange potential is exact. However we use a high temperature approximation to the density matrix and the exchange potential is only approximate. This new quantum molecular dynamics method allows the simulation of collections of quantum particles at finite temperature. Our algorithm can be made to scale linearly with the number of quantum states on which the density matrix is projected. Therefore, it can be optimized to run efficiently on parallel computers. We apply this method to the simulation of the electron plasma in 3-dimensions with different densities (rs = 5.0, 7.5, and 10.0) at various temperatures. Under these conditions, the electron plasma are at the border of the degenerate and the semi-degenerate regimes. The kinetic and potential energies are calculated and compared with results for similar systems simulated with a variational Monte Carlo method. Both results show good agreements with each other at all the densities studied. The quantum path integral molecular dynamics is also employed to study the effect of temperature on the electronic and atomic structural properties of liquid and crystalline alkali metal, namely potassium. In these simulations, ions and valence electrons are treated as classical and quantum particles, respectively. The simple metal undergoes a phase transformation upon heating. Calculated dynamic properties indicate that the atomic motion changes from a vibrational to a diffusive character identifying the transformation as melting. Calculated structural properties further confirm the nature of the transformation. Ionic vibrations in the crystal state and the loss of long range order during melting modify the electronic structure and in particular localize the electrons inside and at the border of the ion core.
Degree ProgramGraduate College