 
Summary: ARTICLES
Quantum Monte Carlo: Direct calculation of corrections to trial wave
functions and their energies
James B. Anderson
Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania 16802
Received 4 January 2000; accepted 10 March 2000
We report an improved Monte Carlo method for calculating the difference between a true wave
function and an analytic trial wave function 0 . The method also produces a correction to the
expectation value of the energy for the trial function. The nodes of the trial function are not
corrected and the energy is corrected to the fixednode energy of the trial function. Applications to
several sample problems as well as to the water molecule are described. © 2000 American
Institute of Physics. S00219606 00 309217
I. INTRODUCTION
We have previously described a quantum Monte Carlo
QMC method for the direct calculation of corrections to
trial wave functions.13
We report here an improved method
which is much simpler to use. Like its predecessors the im
proved method gives for fixed nodes the difference be
tween a true wave function and a trial wave function 0 ,
