External Source Method for Kubo-Transformed Quantum Correlation Functions

摘要

We revisit the external source method for Kubo-transformed quantumcorrelation functions recently proposed by Krishna and Voth. We derive an exactformula and show that the Krishna-Voth formula can be derived as anapproximation of our formula. Some properties of this approximation areclarified through a model calculation of the position autocorrelation functionfor a one-dimensional harmonic oscillator. A key observation is that theKrishna-Voth correlation function has a term which behaves as the secular termin perturbation theory.