OK with Sec IIA
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@ -206,6 +206,7 @@ In Subsec.~\ref{sec:Green}, both the time- and energy-dependent Green's function
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Section \ref{sec:numerical} presents the application of the approach to the one-dimensional Hubbard model.
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Section \ref{sec:numerical} presents the application of the approach to the one-dimensional Hubbard model.
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Finally, in Sec.\ref{sec:conclu}, some conclusions and perspectives are given.
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Finally, in Sec.\ref{sec:conclu}, some conclusions and perspectives are given.
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Atomic units are used throughout.
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Atomic units are used throughout.
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section{Diffusion Monte Carlo}
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\section{Diffusion Monte Carlo}
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\label{sec:DMC}
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\label{sec:DMC}
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@ -262,25 +263,25 @@ Each path is associated with a weight $\prod_{k=0}^{N-1} T_{i_{k} i_{k+1}}$ and
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This expression allows a simple and vivid interpretation of the solution.
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This expression allows a simple and vivid interpretation of the solution.
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In the limit $N \to \infty$, the $i_N$th component of the ground-state wave function (obtained as $\lim_{N \to \infty} G^{(N)}_{i_0 i_N})$ is the weighted sum over all possible paths arriving at vector $\ket{i_N}$.
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In the limit $N \to \infty$, the $i_N$th component of the ground-state wave function (obtained as $\lim_{N \to \infty} G^{(N)}_{i_0 i_N})$ is the weighted sum over all possible paths arriving at vector $\ket{i_N}$.
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This result is independent of the initial vector $\ket{i_0}$, apart from some irrelevant global phase factor. We illustrate this fundamental property pictorially in
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This result is independent of the initial vector $\ket{i_0}$, apart from some irrelevant global phase factor.
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Fig.\ref{fig1}.
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We illustrate this fundamental property pictorially in Fig.~\ref{fig:paths}.
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When the size of the linear space is small, the explicit calculation of the full sums involving $M^N$ terms (where $M$ is the size of the Hilbert space) can be performed.
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When the size of the linear space is small, the explicit calculation of the full sums involving $M^N$ terms (where $M$ is the size of the Hilbert space) can be performed.
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In such a case, we are in the realm of what one would call the ``deterministic'' power methods, such as the Lancz\`os or Davidson approaches.
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In such a case, we are in the realm of what one would call ``deterministic'' power methods, such as the Lancz\`os or Davidson approaches.
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If not, probabilistic techniques for generating only the paths contributing significantly to the sums are to be preferred.
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If not, probabilistic techniques for generating only the paths contributing significantly to the sums are to be preferred.
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This is the central theme of the present work.
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This is the central theme of the present work.
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%%% FIG 0 %%%
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%%% FIG 1 %%%
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\begin{figure}
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\begin{figure*}
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\includegraphics[width=\columnwidth]{fig1}
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\includegraphics[width=0.7\textwidth]{fig1}
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\label{fig:paths}
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\caption{
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\caption{
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\titou{$\Psi$ or $\Phi$?}
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\titou{$\Psi_0$ or $\Phi_0$?}
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Path integral representation of the exact coefficient $c_i=\braket{i}{\Psi_0}$ of the ground-state wave function $\ket{\Psi_0}$ obtained as an infinite sum of paths starting
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Path integral representation of the exact coefficient $c_i=\braket{i}{\Psi_0}$ of the ground-state wave function $\ket{\Psi_0}$ obtained as an infinite sum of paths starting from $\ket{i_0}$ and ending at $\ket{i}$ [see Eq.\eqref{eq:G}].
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from $\ket{i_0}$ and ending at $\ket{i}$ [see Eq.\eqref{eq:G}]. Each path carries a weight $\prod_k T_{i_{k} i_{k+1}}$ computed along the path.
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Each path carries a weight $\prod_k T_{i_{k} i_{k+1}}$ computed along it.
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The result is independent of the choice of the initial state $\ket{i_0}$, provided that $\braket{i_0}{\Psi_0}$ is non-zero.
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The result is independent of the choice of the initial state $\ket{i_0}$, provided that $\braket{i_0}{\Psi_0} \neq 0$.
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Here, only four paths of infinite length have been represented.
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Here, only four paths of infinite length have been represented.
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}
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}
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\label{fig1}
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\end{figure*}
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\end{figure}
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%=======================================%
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%=======================================%
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