[ViewVC] Diff of: group/trunk/tengDissertation/Introduction.tex

Comparing trunk/tengDissertation/Introduction.tex (file contents):
Revision 2685 by tim, Mon Apr 3 18:07:54 2006 UTC vs.
Revision 2696 by tim, Thu Apr 6 22:06:50 2006 UTC

+\chapter{\label{chapt:introduction}INTRODUCTION AND THEORETICAL BACKGROUND}
-<
+\section{\label{introSection:classicalMechanics}Classical Mechanics}
->
+\section{\label{introSection:classicalMechanics}Classical
->
+Mechanics}
-<
+\section{\label{introSection:rigidBody}Dynamics of Rigid Bodies}
->
+Closely related to Classical Mechanics, Molecular Dynamics
->
+simulations are carried out by integrating the equations of motion
->
+for a given system of particles. There are three fundamental ideas
->
+behind classical mechanics. Firstly, One can determine the state of
->
+a mechanical system at any time of interest; Secondly, all the
->
+mechanical properties of the system at that time can be determined
->
+by combining the knowledge of the properties of the system with the
->
+specification of this state; Finally, the specification of the state
->
+when further combine with the laws of mechanics will also be
->
+sufficient to predict the future behavior of the system.
-<
+\section{\label{introSection:statisticalMechanics}Statistical Mechanics}
->
+\subsection{\label{introSection:newtonian}Newtonian Mechanics}
->
+The discovery of Newton's three laws of mechanics which govern the
->
+motion of particles is the foundation of the classical mechanics.
->
+Newton’s first law defines a class of inertial frames. Inertial
->
+frames are reference frames where a particle not interacting with
->
+other bodies will move with constant speed in the same direction.
->
+With respect to inertial frames Newton’s second law has the form
->
+\begin{equation}
->
+F = \frac {dp}{dt} = \frac {mv}{dt}
->
+\label{introEquation:newtonSecondLaw}
->
+\end{equation}
->
+A point mass interacting with other bodies moves with the
->
+acceleration along the direction of the force acting on it. Let
->
+$F_ij$ be the force that particle $i$ exerts on particle $j$, and
->
+$F_ji$ be the force that particle $j$ exerts on particle $i$.
->
+Newton’s third law states that
->
+\begin{equation}
->
+F_ij = -F_ji
->
+ \label{introEquation:newtonThirdLaw}
->
+\end{equation}
-+
+Conservation laws of Newtonian Mechanics play very important roles
-+
+in solving mechanics problems. The linear momentum of a particle is
-+
+conserved if it is free or it experiences no force. The second
-+
+conservation theorem concerns the angular momentum of a particle.
-+
+The angular momentum $L$ of a particle with respect to an origin
-+
+from which $r$ is measured is defined to be
-+
+\begin{equation}
-+
+L \equiv r \times p \label{introEquation:angularMomentumDefinition}
-+
+\end{equation}
-+
+The torque $\tau$ with respect to the same origin is defined to be
-+
+\begin{equation}
-+
+N \equiv r \times F \label{introEquation:torqueDefinition}
-+
+\end{equation}
-+
+Differentiating Eq.~\ref{introEquation:angularMomentumDefinition},
-+
+\[
-+
+\dot L = \frac{d}{{dt}}(r \times p) = (\dot r \times p) + (r \times
-+
+\dot p)
-+
+\]
-+
+since
-+
+\[
-+
+\dot r \times p = \dot r \times mv = m\dot r \times \dot r \equiv 0
-+
+\]
-+
+thus,
-+
+\begin{equation}
-+
+\dot L = r \times \dot p = N
-+
+\end{equation}
-+
+If there are no external torques acting on a body, the angular
-+
+momentum of it is conserved. The last conservation theorem state
-+
+that if all forces are conservative, Energy
-+
+\begin{equation}E = T + V \label{introEquation:energyConservation}
-+
+\end{equation}
-+
+ is conserved. All of these conserved quantities are
-+
+important factors to determine the quality of numerical integration
-+
+scheme for rigid body \cite{Dullweber1997}.
-+
-+
+\subsection{\label{introSection:lagrangian}Lagrangian Mechanics}
-+
-+
+Newtonian Mechanics suffers from two important limitations: it
-+
+describes their motion in special cartesian coordinate systems.
-+
+Another limitation of Newtonian mechanics becomes obvious when we
-+
+try to describe systems with large numbers of particles. It becomes
-+
+very difficult to predict the properties of the system by carrying
-+
+out calculations involving the each individual interaction between
-+
+all the particles, even if we know all of the details of the
-+
+interaction. In order to overcome some of the practical difficulties
-+
+which arise in attempts to apply Newton's equation to complex
-+
+system, alternative procedures may be developed.
-+
-+
+\subsubsection{\label{introSection:halmiltonPrinciple}Hamilton's
-+
+Principle}
-+
-+
+Hamilton introduced the dynamical principle upon which it is
-+
+possible to base all of mechanics and, indeed, most of classical
-+
+physics. Hamilton's Principle may be stated as follow,
-+
-+
+The actual trajectory, along which a dynamical system may move from
-+
+one point to another within a specified time, is derived by finding
-+
+the path which minimizes the time integral of the difference between
-+
+the kinetic, $K$, and potential energies, $U$ \cite{tolman79}.
-+
+\begin{equation}
-+
+\delta \int_{t_1 }^{t_2 } {(K - U)dt = 0} ,
-+
+\label{introEquation:halmitonianPrinciple1}
-+
+\end{equation}
-+
-+
+For simple mechanical systems, where the forces acting on the
-+
+different part are derivable from a potential and the velocities are
-+
+small compared with that of light, the Lagrangian function $L$ can
-+
+be define as the difference between the kinetic energy of the system
-+
+and its potential energy,
-+
+\begin{equation}
-+
+L \equiv K - U = L(q_i ,\dot q_i ) ,
-+
+\label{introEquation:lagrangianDef}
-+
+\end{equation}
-+
+then Eq.~\ref{introEquation:halmitonianPrinciple1} becomes
-+
+\begin{equation}
-+
+\delta \int_{t_1 }^{t_2 } {L dt = 0} ,
-+
+\label{introEquation:halmitonianPrinciple2}
-+
+\end{equation}
-+
-+
+\subsubsection{\label{introSection:equationOfMotionLagrangian}The
-+
+Equations of Motion in Lagrangian Mechanics}
-+
-+
+for a holonomic system of $f$ degrees of freedom, the equations of
-+
+motion in the Lagrangian form is
-+
+\begin{equation}
-+
+\frac{d}{{dt}}\frac{{\partial L}}{{\partial \dot q_i }} -
-+
+\frac{{\partial L}}{{\partial q_i }} = 0,{\rm{ }}i = 1, \ldots,f
-+
+\label{introEquation:eqMotionLagrangian}
-+
+\end{equation}
-+
+where $q_{i}$ is generalized coordinate and $\dot{q_{i}}$ is
-+
+generalized velocity.
-+
-+
+\subsection{\label{introSection:hamiltonian}Hamiltonian Mechanics}
-+
-+
+Arising from Lagrangian Mechanics, Hamiltonian Mechanics was
-+
+introduced by William Rowan Hamilton in 1833 as a re-formulation of
-+
+classical mechanics. If the potential energy of a system is
-+
+independent of generalized velocities, the generalized momenta can
-+
+be defined as
-+
+\begin{equation}
-+
+p_i = \frac{\partial L}{\partial \dot q_i}
-+
+\label{introEquation:generalizedMomenta}
-+
+\end{equation}
-+
+The Lagrange equations of motion are then expressed by
-+
+\begin{equation}
-+
+p_i  = \frac{{\partial L}}{{\partial q_i }}
-+
+\label{introEquation:generalizedMomentaDot}
-+
+\end{equation}
-+
-+
+With the help of the generalized momenta, we may now define a new
-+
+quantity $H$ by the equation
-+
+\begin{equation}
-+
+H = \sum\limits_k {p_k \dot q_k }  - L ,
-+
+\label{introEquation:hamiltonianDefByLagrangian}
-+
+\end{equation}
-+
+where $ \dot q_1  \ldots \dot q_f $ are generalized velocities and
-+
+$L$ is the Lagrangian function for the system.
-+
-+
+Differentiating Eq.~\ref{introEquation:hamiltonianDefByLagrangian},
-+
+one can obtain
-+
+\begin{equation}
-+
+dH = \sum\limits_k {\left( {p_k d\dot q_k  + \dot q_k dp_k  -
-+
+\frac{{\partial L}}{{\partial q_k }}dq_k  - \frac{{\partial
-+
+L}}{{\partial \dot q_k }}d\dot q_k } \right)}  - \frac{{\partial
-+
+L}}{{\partial t}}dt \label{introEquation:diffHamiltonian1}
-+
+\end{equation}
-+
+Making use of  Eq.~\ref{introEquation:generalizedMomenta}, the
-+
+second and fourth terms in the parentheses cancel. Therefore,
-+
+Eq.~\ref{introEquation:diffHamiltonian1} can be rewritten as
-+
+\begin{equation}
-+
+dH = \sum\limits_k {\left( {\dot q_k dp_k  - \dot p_k dq_k }
-+
+\right)}  - \frac{{\partial L}}{{\partial t}}dt
-+
+\label{introEquation:diffHamiltonian2}
-+
+\end{equation}
-+
+By identifying the coefficients of $dq_k$, $dp_k$ and dt, we can
-+
+find
-+
+\begin{equation}
-+
+\frac{{\partial H}}{{\partial p_k }} = q_k
-+
+\label{introEquation:motionHamiltonianCoordinate}
-+
+\end{equation}
-+
+\begin{equation}
-+
+\frac{{\partial H}}{{\partial q_k }} =  - p_k
-+
+\label{introEquation:motionHamiltonianMomentum}
-+
+\end{equation}
-+
+and
-+
+\begin{equation}
-+
+\frac{{\partial H}}{{\partial t}} =  - \frac{{\partial L}}{{\partial
-+
+t}}
-+
+\label{introEquation:motionHamiltonianTime}
-+
+\end{equation}
-+
-+
+Eq.~\ref{introEquation:motionHamiltonianCoordinate} and
-+
+Eq.~\ref{introEquation:motionHamiltonianMomentum} are Hamilton's
-+
+equation of motion. Due to their symmetrical formula, they are also
-+
+known as the canonical equations of motions \cite{Goldstein01}.
-+
-+
+An important difference between Lagrangian approach and the
-+
+Hamiltonian approach is that the Lagrangian is considered to be a
-+
+function of the generalized velocities $\dot q_i$ and the
-+
+generalized coordinates $q_i$, while the Hamiltonian is considered
-+
+to be a function of the generalized momenta $p_i$ and the conjugate
-+
+generalized coordinate $q_i$. Hamiltonian Mechanics is more
-+
+appropriate for application to statistical mechanics and quantum
-+
+mechanics, since it treats the coordinate and its time derivative as
-+
+independent variables and it only works with 1st-order differential
-+
+equations\cite{Marion90}.
-+
-+
+In Newtonian Mechanics, a system described by conservative forces
-+
+conserves the total energy \ref{introEquation:energyConservation}.
-+
+It follows that Hamilton's equations of motion conserve the total
-+
+Hamiltonian.
-+
+\begin{equation}
-+
+\frac{{dH}}{{dt}} = \sum\limits_i {\left( {\frac{{\partial
-+
+H}}{{\partial q_i }}\dot q_i  + \frac{{\partial H}}{{\partial p_i
-+
+}}\dot p_i } \right)}  = \sum\limits_i {\left( {\frac{{\partial
-+
+H}}{{\partial q_i }}\frac{{\partial H}}{{\partial p_i }} -
-+
+\frac{{\partial H}}{{\partial p_i }}\frac{{\partial H}}{{\partial
-+
+q_i }}} \right) = 0}
-+
+\label{introEquation:conserveHalmitonian}
-+
+\end{equation}
-+
-+
+When studying Hamiltonian system, it is more convenient to use
-+
+notation
-+
+\begin{equation}
-+
+r = r(q,p)^T
-+
+\end{equation}
-+
+and to introduce a $2n \times 2n$ canonical structure matrix $J$,
-+
+\begin{equation}
-+
+J = \left( {\begin{array}{*{20}c}
-+
+& I  \\
-+
+   { - I} & 0  \\
-+
+\end{array}} \right)
-+
+\label{introEquation:canonicalMatrix}
-+
+\end{equation}
-+
+where $I$ is a $n \times n$ identity matrix and $J$ is a
-+
+skew-symmetric matrix ($ J^T  =  - J $). Thus, Hamiltonian system
-+
+can be rewritten as,
-+
+\begin{equation}
-+
+\frac{d}{{dt}}r = J\nabla _r H(r)
-+
+\label{introEquation:compactHamiltonian}
-+
+\end{equation}
-+
-+
+\section{\label{introSection:geometricIntegratos}Geometric Integrators}
-+
-+
+\subsection{\label{introSection:symplecticManifold}Symplectic Manifold}
-+
+A \emph{manifold} is an abstract mathematical space. It locally
-+
+looks like Euclidean space, but when viewed globally, it may have
-+
+more complicate structure. A good example of manifold is the surface
-+
+of Earth. It seems to be flat locally, but it is round if viewed as
-+
+a whole. A \emph{differentiable manifold} (also known as
-+
+\emph{smooth manifold}) is a manifold with an open cover in which
-+
+the covering neighborhoods are all smoothly isomorphic to one
-+
+another. In other words,it is possible to apply calculus on
-+
+\emph{differentiable manifold}. A \emph{symplectic manifold} is
-+
+defined as a pair $(M, \omega)$ consisting of a \emph{differentiable
-+
+manifold} $M$ and a close, non-degenerated, bilinear symplectic
-+
+form, $\omega$. One of the motivation to study \emph{symplectic
-+
+manifold} in Hamiltonian Mechanics is that a symplectic manifold can
-+
+represent all possible configurations of the system and the phase
-+
+space of the system can be described by it's cotangent bundle. Every
-+
+symplectic manifold is even dimensional. For instance, in Hamilton
-+
+equations, coordinate and momentum always appear in pairs.
-+
-+
+A \emph{symplectomorphism} is also known as a \emph{canonical
-+
+transformation}.
-+
-+
+Any real-valued differentiable function H on a symplectic manifold
-+
+can serve as an energy function or Hamiltonian. Associated to any
-+
+Hamiltonian is a Hamiltonian vector field; the integral curves of
-+
+the Hamiltonian vector field are solutions to the Hamilton-Jacobi
-+
+equations. The Hamiltonian vector field defines a flow on the
-+
+symplectic manifold, called a Hamiltonian flow or symplectomorphism.
-+
+By Liouville's theorem, Hamiltonian flows preserve the volume form
-+
+on the phase space.
-+
-+
+\subsection{\label{Construction of Symplectic Methods}}
-+
-+
+\section{\label{introSection:statisticalMechanics}Statistical
-+
+Mechanics}
-+
-+
+The thermodynamic behaviors and properties of Molecular Dynamics
-+
+simulation are governed by the principle of Statistical Mechanics.
-+
+The following section will give a brief introduction to some of the
-+
+Statistical Mechanics concepts presented in this dissertation.
-+
-+
+\subsection{\label{introSection:ensemble}Ensemble and Phase Space}
-+
-+
+\subsection{\label{introSection:ergodic}The Ergodic Hypothesis}
-+
-+
+Various thermodynamic properties can be calculated from Molecular
-+
+Dynamics simulation. By comparing experimental values with the
-+
+calculated properties, one can determine the accuracy of the
-+
+simulation and the quality of the underlying model. However, both of
-+
+experiment and computer simulation are usually performed during a
-+
+certain time interval and the measurements are averaged over a
-+
+period of them which is different from the average behavior of
-+
+many-body system in Statistical Mechanics. Fortunately, Ergodic
-+
+Hypothesis is proposed to make a connection between time average and
-+
+ensemble average. It states that time average and average over the
-+
+statistical ensemble are identical \cite{Frenkel1996, leach01:mm}.
-+
+\begin{equation}
-+
+\langle A \rangle_t = \mathop {\lim }\limits_{t \to \infty }
-+
+\frac{1}{t}\int\limits_0^t {A(p(t),q(t))dt = \int\limits_\Gamma
-+
+{A(p(t),q(t))} } \rho (p(t), q(t)) dpdq
-+
+\end{equation}
-+
+where $\langle A \rangle_t$ is an equilibrium value of a physical
-+
+quantity and $\rho (p(t), q(t))$ is the equilibrium distribution
-+
+function. If an observation is averaged over a sufficiently long
-+
+time (longer than relaxation time), all accessible microstates in
-+
+phase space are assumed to be equally probed, giving a properly
-+
+weighted statistical average. This allows the researcher freedom of
-+
+choice when deciding how best to measure a given observable. In case
-+
+an ensemble averaged approach sounds most reasonable, the Monte
-+
+Carlo techniques\cite{metropolis:1949} can be utilized. Or if the
-+
+system lends itself to a time averaging approach, the Molecular
-+
+Dynamics techniques in Sec.~\ref{introSection:molecularDynamics}
-+
+will be the best choice\cite{Frenkel1996}.
-+
+\section{\label{introSection:molecularDynamics}Molecular Dynamics}
-+
+As a special discipline of molecular modeling, Molecular dynamics
-+
+has proven to be a powerful tool for studying the functions of
-+
+biological systems, providing structural, thermodynamic and
-+
+dynamical information.
-+
-+
+\subsection{\label{introSec:mdInit}Initialization}
-+
-+
+\subsection{\label{introSection:mdIntegration} Integration of the Equations of Motion}
-+
-+
+\section{\label{introSection:rigidBody}Dynamics of Rigid Bodies}
-+
-+
+A rigid body is a body in which the distance between any two given
-+
+points of a rigid body remains constant regardless of external
-+
+forces exerted on it. A rigid body therefore conserves its shape
-+
+during its motion.
-+
-+
+Applications of dynamics of rigid bodies.
-+
-+
+\subsection{\label{introSection:lieAlgebra}Lie Algebra}
-+
-+
+\subsection{\label{introSection:DLMMotionEquation}The Euler Equations of Rigid Body Motion}
-+
-+
+\subsection{\label{introSection:otherRBMotionEquation}Other Formulations for Rigid Body Motion}
-+
-+
+%\subsection{\label{introSection:poissonBrackets}Poisson Brackets}
-+
-+
+\section{\label{introSection:correlationFunctions}Correlation Functions}
-+
+\section{\label{introSection:langevinDynamics}Langevin Dynamics}
-+
+\subsection{\label{introSection:LDIntroduction}Introduction and application of Langevin Dynamics}
-+
-+
+\subsection{\label{introSection:generalizedLangevinDynamics}Generalized Langevin Dynamics}
-+
-+
+\begin{equation}
-+
+H = \frac{{p^2 }}{{2m}} + U(x) + H_B  + \Delta U(x,x_1 , \ldots x_N)
-+
+\label{introEquation:bathGLE}
-+
+\end{equation}
-+
+where $H_B$ is harmonic bath Hamiltonian,
-+
+\[
-+
+H_B  =\sum\limits_{\alpha  = 1}^N {\left\{ {\frac{{p_\alpha ^2
-+
+}}{{2m_\alpha  }} + \frac{1}{2}m_\alpha  w_\alpha ^2 } \right\}}
-+
+\]
-+
+and $\Delta U$ is bilinear system-bath coupling,
-+
+\[
-+
+\Delta U =  - \sum\limits_{\alpha  = 1}^N {g_\alpha  x_\alpha  x}
-+
+\]
-+
+Completing the square,
-+
+\[
-+
+H_B  + \Delta U = \sum\limits_{\alpha  = 1}^N {\left\{
-+
+{\frac{{p_\alpha ^2 }}{{2m_\alpha  }} + \frac{1}{2}m_\alpha
-+
+w_\alpha ^2 \left( {x_\alpha   - \frac{{g_\alpha  }}{{m_\alpha
-+
+w_\alpha ^2 }}x} \right)^2 } \right\}}  - \sum\limits_{\alpha  =
-+
+}^N {\frac{{g_\alpha ^2 }}{{2m_\alpha  w_\alpha ^2 }}} x^2
-+
+\]
-+
+and putting it back into Eq.~\ref{introEquation:bathGLE},
-+
+\[
-+
+H = \frac{{p^2 }}{{2m}} + W(x) + \sum\limits_{\alpha  = 1}^N
-+
+{\left\{ {\frac{{p_\alpha ^2 }}{{2m_\alpha  }} + \frac{1}{2}m_\alpha
-+
+w_\alpha ^2 \left( {x_\alpha   - \frac{{g_\alpha  }}{{m_\alpha
-+
+w_\alpha ^2 }}x} \right)^2 } \right\}}
-+
+\]
-+
+where
-+
+\[
-+
+W(x) = U(x) - \sum\limits_{\alpha  = 1}^N {\frac{{g_\alpha ^2
-+
+}}{{2m_\alpha  w_\alpha ^2 }}} x^2
-+
+\]
-+
+Since the first two terms of the new Hamiltonian depend only on the
-+
+system coordinates, we can get the equations of motion for
-+
+Generalized Langevin Dynamics by Hamilton's equations
-+
+\ref{introEquation:motionHamiltonianCoordinate,
-+
+introEquation:motionHamiltonianMomentum},
-+
+\begin{align}
-+
+\dot p &=  - \frac{{\partial H}}{{\partial x}}
-+
+       &= m\ddot x
-+
+       &= - \frac{{\partial W(x)}}{{\partial x}} - \sum\limits_{\alpha  = 1}^N {g_\alpha  \left( {x_\alpha   - \frac{{g_\alpha  }}{{m_\alpha  w_\alpha ^2 }}x} \right)}
-+
+\label{introEq:Lp5}
-+
+\end{align}
-+
+, and
-+
+\begin{align}
-+
+\dot p_\alpha   &=  - \frac{{\partial H}}{{\partial x_\alpha  }}
-+
+                &= m\ddot x_\alpha
-+
+                &= \- m_\alpha  w_\alpha ^2 \left( {x_\alpha   - \frac{{g_\alpha}}{{m_\alpha  w_\alpha ^2 }}x} \right)
-+
+\end{align}
-+
-+
+\subsection{\label{introSection:laplaceTransform}The Laplace Transform}
-+
-+
+\[
-+
+L(x) = \int_0^\infty  {x(t)e^{ - pt} dt}
-+
+\]
-+
-+
+\[
-+
+L(x + y) = L(x) + L(y)
-+
+\]
-+
-+
+\[
-+
+L(ax) = aL(x)
-+
+\]
-+
-+
+\[
-+
+L(\dot x) = pL(x) - px(0)
-+
+\]
-+
-+
+\[
-+
+L(\ddot x) = p^2 L(x) - px(0) - \dot x(0)
-+
+\]
-+
-+
+\[
-+
+L\left( {\int_0^t {g(t - \tau )h(\tau )d\tau } } \right) = G(p)H(p)
-+
+\]
-+
-+
+Some relatively important transformation,
-+
+\[
-+
+L(\cos at) = \frac{p}{{p^2  + a^2 }}
-+
+\]
-+
-+
+\[
-+
+L(\sin at) = \frac{a}{{p^2  + a^2 }}
-+
+\]
-+
-+
+\[
-+
+L(1) = \frac{1}{p}
-+
+\]
-+
-+
+First, the bath coordinates,
-+
+\[
-+
+p^2 L(x_\alpha  ) - px_\alpha  (0) - \dot x_\alpha  (0) =  - \omega
-+
+_\alpha ^2 L(x_\alpha  ) + \frac{{g_\alpha  }}{{\omega _\alpha
-+
+}}L(x)
-+
+\]
-+
+\[
-+
+L(x_\alpha  ) = \frac{{\frac{{g_\alpha  }}{{\omega _\alpha  }}L(x) +
-+
+px_\alpha  (0) + \dot x_\alpha  (0)}}{{p^2  + \omega _\alpha ^2 }}
-+
+\]
-+
+Then, the system coordinates,
-+
+\begin{align}
-+
+mL(\ddot x) &=  - \frac{1}{p}\frac{{\partial W(x)}}{{\partial x}} -
-+
+\sum\limits_{\alpha  = 1}^N {\left\{ {\frac{{\frac{{g_\alpha
-+
+}}{{\omega _\alpha  }}L(x) + px_\alpha  (0) + \dot x_\alpha
-+
+(0)}}{{p^2  + \omega _\alpha ^2 }} - \frac{{g_\alpha ^2 }}{{m_\alpha
-+
+}}\omega _\alpha ^2 L(x)} \right\}}
-+
+%
-+
+ &= - \frac{1}{p}\frac{{\partial W(x)}}{{\partial x}} -
-+
+ \sum\limits_{\alpha  = 1}^N {\left\{ { - \frac{{g_\alpha ^2 }}{{m_\alpha  \omega _\alpha ^2 }}\frac{p}{{p^2  + \omega _\alpha ^2 }}pL(x)
-+
+ - \frac{p}{{p^2  + \omega _\alpha ^2 }}g_\alpha  x_\alpha  (0)
-+
+ - \frac{1}{{p^2  + \omega _\alpha ^2 }}g_\alpha  \dot x_\alpha  (0)} \right\}}
-+
+\end{align}
-+
+Then, the inverse transform,
-+
-+
+\begin{align}
-+
+m\ddot x &=  - \frac{{\partial W(x)}}{{\partial x}} -
-+
+\sum\limits_{\alpha  = 1}^N {\left\{ {\left( { - \frac{{g_\alpha ^2
-+
+}}{{m_\alpha  \omega _\alpha ^2 }}} \right)\int_0^t {\cos (\omega
-+
+_\alpha  t)\dot x(t - \tau )d\tau  - \left[ {g_\alpha  x_\alpha  (0)
-+
+- \frac{{g_\alpha  }}{{m_\alpha  \omega _\alpha  }}} \right]\cos
-+
+(\omega _\alpha  t) - \frac{{g_\alpha  \dot x_\alpha  (0)}}{{\omega
-+
+_\alpha  }}\sin (\omega _\alpha  t)} } \right\}}
-+
+%
-+
+&= - \frac{{\partial W(x)}}{{\partial x}} - \int_0^t
-+
+{\sum\limits_{\alpha  = 1}^N {\left( { - \frac{{g_\alpha ^2
-+
+}}{{m_\alpha  \omega _\alpha ^2 }}} \right)\cos (\omega _\alpha
-+
+t)\dot x(t - \tau )d} \tau }  + \sum\limits_{\alpha  = 1}^N {\left\{
-+
+{\left[ {g_\alpha  x_\alpha  (0) - \frac{{g_\alpha  }}{{m_\alpha
-+
+\omega _\alpha  }}} \right]\cos (\omega _\alpha  t) +
-+
+\frac{{g_\alpha  \dot x_\alpha  (0)}}{{\omega _\alpha  }}\sin
-+
+(\omega _\alpha  t)} \right\}}
-+
+\end{align}
-+
-+
+\begin{equation}
-+
+m\ddot x =  - \frac{{\partial W}}{{\partial x}} - \int_0^t {\xi
-+
+(t)\dot x(t - \tau )d\tau }  + R(t)
-+
+\label{introEuqation:GeneralizedLangevinDynamics}
-+
+\end{equation}
-+
+%where $ {\xi (t)}$ is friction kernel, $R(t)$ is random force and
-+
+%$W$ is the potential of mean force. $W(x) =  - kT\ln p(x)$
-+
+\[
-+
+\xi (t) = \sum\limits_{\alpha  = 1}^N {\left( { - \frac{{g_\alpha ^2
-+
+}}{{m_\alpha  \omega _\alpha ^2 }}} \right)\cos (\omega _\alpha  t)}
-+
+\]
-+
+For an infinite harmonic bath, we can use the spectral density and
-+
+an integral over frequencies.
-+
-+
+\[
-+
+R(t) = \sum\limits_{\alpha  = 1}^N {\left( {g_\alpha  x_\alpha  (0)
-+
+- \frac{{g_\alpha ^2 }}{{m_\alpha  \omega _\alpha ^2 }}x(0)}
-+
+\right)\cos (\omega _\alpha  t)}  + \frac{{\dot x_\alpha
-+
+(0)}}{{\omega _\alpha  }}\sin (\omega _\alpha  t)
-+
+\]
-+
+The random forces depend only on initial conditions.
-+
-+
+\subsubsection{\label{introSection:secondFluctuationDissipation}The Second Fluctuation Dissipation Theorem}
-+
+So we can define a new set of coordinates,
-+
+\[
-+
+q_\alpha  (t) = x_\alpha  (t) - \frac{1}{{m_\alpha  \omega _\alpha
-+
+^2 }}x(0)
-+
+\]
-+
+This makes
-+
+\[
-+
+R(t) = \sum\limits_{\alpha  = 1}^N {g_\alpha  q_\alpha  (t)}
-+
+\]
-+
+And since the $q$ coordinates are harmonic oscillators,
-+
+\[
-+
+\begin{array}{l}
-+
+ \left\langle {q_\alpha  (t)q_\alpha  (0)} \right\rangle  = \left\langle {q_\alpha ^2 (0)} \right\rangle \cos (\omega _\alpha  t) \\
-+
+ \left\langle {q_\alpha  (t)q_\beta  (0)} \right\rangle  = \delta _{\alpha \beta } \left\langle {q_\alpha  (t)q_\alpha  (0)} \right\rangle  \\
-+
+ \end{array}
-+
+\]
-+
-+
+\begin{align}
-+
+\left\langle {R(t)R(0)} \right\rangle  &= \sum\limits_\alpha
-+
+{\sum\limits_\beta  {g_\alpha  g_\beta  \left\langle {q_\alpha
-+
+(t)q_\beta  (0)} \right\rangle } }
-+
+%
-+
+&= \sum\limits_\alpha  {g_\alpha ^2 \left\langle {q_\alpha ^2 (0)}
-+
+\right\rangle \cos (\omega _\alpha  t)}
-+
+%
-+
+&= kT\xi (t)
-+
+\end{align}
-+
-+
+\begin{equation}
-+
+\xi (t) = \left\langle {R(t)R(0)} \right\rangle
-+
+\label{introEquation:secondFluctuationDissipation}
-+
+\end{equation}
-+
+\section{\label{introSection:hydroynamics}Hydrodynamics}
-<
+\section{\label{introSection:correlationFunctions}Correlation Functions}
->
+\subsection{\label{introSection:frictionTensor} Friction Tensor}
->
+\subsection{\label{introSection:analyticalApproach}Analytical
->
+Approach}
->
->
+\subsection{\label{introSection:approximationApproach}Approximation
->
+Approach}
->
->
+\subsection{\label{introSection:centersRigidBody}Centers of Rigid
->
+Body}

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing trunk/tengDissertation/Introduction.tex (file contents): Revision 2685 by tim, Mon Apr 3 18:07:54 2006 UTC vs. Revision 2696 by tim, Thu Apr 6 22:06:50 2006 UTC

Diff Legend

Comparing trunk/tengDissertation/Introduction.tex (file contents):
Revision 2685 by tim, Mon Apr 3 18:07:54 2006 UTC vs.
Revision 2696 by tim, Thu Apr 6 22:06:50 2006 UTC