OK with Sec IIA

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Pierre-Francois Loos 2022-10-03 11:15:41 +02:00
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@ -206,6 +206,7 @@ In Subsec.~\ref{sec:Green}, both the time- and energy-dependent Green's function
Section \ref{sec:numerical} presents the application of the approach to the one-dimensional Hubbard model. Section \ref{sec:numerical} presents the application of the approach to the one-dimensional Hubbard model.
Finally, in Sec.\ref{sec:conclu}, some conclusions and perspectives are given. Finally, in Sec.\ref{sec:conclu}, some conclusions and perspectives are given.
Atomic units are used throughout. Atomic units are used throughout.
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\section{Diffusion Monte Carlo} \section{Diffusion Monte Carlo}
\label{sec:DMC} \label{sec:DMC}
@ -262,25 +263,25 @@ Each path is associated with a weight $\prod_{k=0}^{N-1} T_{i_{k} i_{k+1}}$ and
This expression allows a simple and vivid interpretation of the solution. This expression allows a simple and vivid interpretation of the solution.
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 $\ket{i_N}$. 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 $\ket{i_N}$.
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 This result is independent of the initial vector $\ket{i_0}$, apart from some irrelevant global phase factor.
Fig.\ref{fig1}. We illustrate this fundamental property pictorially in Fig.~\ref{fig:paths}.
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. 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.
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. 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.
If not, probabilistic techniques for generating only the paths contributing significantly to the sums are to be preferred. If not, probabilistic techniques for generating only the paths contributing significantly to the sums are to be preferred.
This is the central theme of the present work. This is the central theme of the present work.
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\begin{figure} \begin{figure*}
\includegraphics[width=\columnwidth]{fig1} \includegraphics[width=0.7\textwidth]{fig1}
\label{fig:paths}
\caption{ \caption{
\titou{$\Psi$ or $\Phi$?} \titou{$\Psi_0$ or $\Phi_0$?}
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 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}].
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. Each path carries a weight $\prod_k T_{i_{k} i_{k+1}}$ computed along it.
The result is independent of the choice of the initial state $\ket{i_0}$, provided that $\braket{i_0}{\Psi_0}$ is non-zero. The result is independent of the choice of the initial state $\ket{i_0}$, provided that $\braket{i_0}{\Psi_0} \neq 0$.
Here, only four paths of infinite length have been represented. Here, only four paths of infinite length have been represented.
} }
\label{fig1} \end{figure*}
\end{figure}
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