--- trunk/chrisDissertation/dissertation.tex 2006/09/22 13:45:24 3019 +++ trunk/chrisDissertation/dissertation.tex 2006/09/26 03:07:59 3023 @@ -16,7 +16,7 @@ \frontmatter -\title{APPLICATION AND DEVELOPMENT OF MOLECULAR DYNAMICS TECHNIQUES FOR THE +\title{DEVELOPMENT OF MOLECULAR DYNAMICS TECHNIQUES FOR THE STUDY OF WATER AND OTHER BIOCHEMICAL SYSTEMS} \author{Christopher Joseph Fennell} \work{Dissertation} @@ -29,34 +29,69 @@ STUDY OF WATER AND OTHER BIOCHEMICAL SYSTEMS} \begin{abstract} -The following dissertation lays out research that I have performed -over the last several years. All of the work relies on the technique of -molecular dynamics, and in this dissertation I start by outlining many -of the considerations that go into molecular dynamics -simulations. This is followed by an introduction to {\sc oopse}, the -object oriented parallel simulation engine, which is a program for -performing molecular simulations developed and maintained in our -lab. Most of the research was performed either using {\sc oopse} or -earlier code that predated {\sc oopse}. +This dissertation comprises a body of research in the field of +classical molecular simulations, with particular emphasis placed on +the proper depiction of water. This work is arranged such that the +techniques and models used within are first developed and tested +before being applied and compared with experimental results. With this +organization in mind, it is appropriate that the first chapter deals +primarily the technique of molecular dynamics and technical +considerations needed to correctly perform molecular simulations. -This introduction is followed by three chapters that discuss in detail -the primary research projects for which I am responsible. The first -project discusses my work on electrostatic interaction correction -techniques, with applications to water and biologically relevant -molecular systems. This leads into work on improving the depiction of -water in molecular simulations by refining simple and highly -computationally efficient single point water models. The final project -discussed in this body of research involves free energy calculations -of ice polymorphs, and includes investigations of a new ice polymorph -that we discovered while performing simulations involving the single -point water models. +Building on this framework, the second chapter discusses correction +techniques for handling the long-ranged electrostatic interactions +common in molecular simulations. Particular focus is placed on a +shifted-force ({\sc sf}) modification of the damped shifted Coulombic +summation method. In this work, {\sc sf} is shown to be nearly +equivalent to the more commonly utilized Ewald summation in +simulations of condensed phases. Since the {\sc sf} technique is +pairwise, it scales as $\mathcal{O}(N)$ and lacks periodicity +artifacts introduced through heavy reliance on the reciprocal-space +portion of the Ewald sum. The electrostatic damping technique used +with {\sc sf} is then extended beyond simple charge-charge +interactions to include point-multipoles. Optimal damping parameter +settings are also determined to ensure proper depiction of the +dielectric behavior of molecular systems. Presenting this technique +early enables its application in the systems discussed in the later +chapters and shows how it can improve the quality of various molecular +simulations. -I end this dissertation with some concluding remarks and -appendices. The conclusion simply sums up the previous sections and -comments on the research findings. The appendices include supporting -information and a more detailed look at systems that were treated in a -more general form in the earlier sections. +The third chapter applies the above techniques and focuses on water +model development, specifically the single-point soft sticky dipole +(SSD) model. In order to better depict water with SSD in computer +simulations, it needed to be reparametrized. This work results in the +development of SSD/RF and SSD/E, new variants of the SSD model +optimized for simulations with and without a reaction field +correction. These new single-point models are more efficient than the +common multi-point partial charge models and better capture the +dynamic properties of water. SSD/RF can be successfully used with +damped {\sc sf} through the multipolar extension of the technique +described in the previous chapter. Discussion on the development of +the two-point tetrahedrally restructured elongated dipole (TRED) water +model is also presented, and this model is optimized for use with the +damped {\sc sf} technique. Though there remain some algorithmic +complexities that need to be addressed (logic for neglecting +charge-quadrupole interactions between other TRED molecules) to use +this model in general simulations, it is approximately twice as +efficient as the commonly used three-point water models (i.e. TIP3P +and SPC/E). +Continuing in the direction of model applications, the final chapter +deals with a unique polymorph of ice that was discovered while +performing water simulations with the fast simple water models +discussed in the previous chapter. This form of ice, called +``imaginary ice'' (Ice-$i$), has a low-density structure which is +different from any known polymorph observed in either experiment or +computer simulation studies. The free energy analysis discussed here +shows that this structure is in fact the thermodynamically preferred +form of ice for both the single-point and commonly used multi-point +water models under the chosen simulation conditions. It is shown that +inclusion of electrostatic corrections is necessary to obtain more +realistic results; however, the free energies of the various +polymorphs (both imaginary and real) in many of these models is shown +to be so similar that choice of system properties, like the volume in +$NVT$ simulations, can directly influence the ice polymorph expressed. + \end{abstract} \begin{dedication} @@ -78,9 +113,9 @@ Edward P.~Fennell and Rosalie M.~Fennell, for providin thank Christopher Harrison and Dr. Steven Corcelli for additional discussions and comments. Finally, I would like to thank my parents, Edward P.~Fennell and Rosalie M.~Fennell, for providing the -opprotunities and encouragement that allowed me to pursue my +opportunities and encouragement that allowed me to pursue my interests, and I would like to thank my wife, Kelley, for her -unwaivering support. +unwavering support. \end{acknowledge} \mainmatter