Mixed Quantum-Classical Molecular Dynamics Study of a Hydrated Electron and an Investigation of Temperature Control Algorithms
Date of Award
Doctor of Philosophy (PhD)
Stuart, Steven J
McNeill , Jason
Latourr , Robert
Dominy , Brian
The use of classical and quantum mechanics has been employed in this dissertation to study temperature control algorithms and a hydrated electron. A comparison of the effects of four commonly used temperature control algorithms on the energetics and dynamics of liquid water has been executed, in efforts to better understand the non-equipartitioning effects caused by some thermostats. The Berendsen, Andersen, Langevin, and velocity rescaling temperature control algorithms were applied to both dimer and bulk water systems, using the TIP4P water model. The two deterministic thermostats, Berendsen and velocity rescaling, display the 'flying ice cube effect' that had been noticed earlier for the velocity rescaling thermostat (S.C. Harvey et al, J. Comp. Chem. 19, 727 (1998)). Specifically, these thermostats lead to violation of energy equipartition, with the rotational temperature much colder and the translational temperature much hotter than the mean temperature. The two stochastic thermostats, on the other hand, Andersen and Langevin, both lead to correct, equilibrium equipartitioning of the system energy. The computational details and simulation results are discussed in Chapter 2, and specific thermostat algorithms are discussed in Chapter 1, Section 1.1.
The effects of different water models on the physical properties of a hydrated electron have been studied. Prior simulation studies have been performed primarily with the SPC-FLEX water model, and have resulted in only partial agreement with experiment. Consequently, it is of considerable interest to determine whether the choice of water model has a large effect on the properties of the hydrated electron. Properties such as the energy of the ground state wavefunction, radius of gyration of the electron, and the absorption spectrum were calculated from adiabatic dynamics simulations of a single electron hydrated by SPC, TIP4P and TIP4P-FQ water. We observed that the choice of water model significantly affects the energetics and dynamics of the hydrated electron. We also found that the absorption spectra of the hydrated electron solvated in both polarizable and nonpolarizable water using the Rossky electron water Pseudopotential, continues to be blue-shifted. The computational details and simulation results are discussed in Chapter 3, and Chapter 4.
Aremu-cole, Janet, "Mixed Quantum-Classical Molecular Dynamics Study of a Hydrated Electron and an Investigation of Temperature Control Algorithms" (2007). All Dissertations. 104.