*Email Address: *srothste@abacus.ac.brocku.ca

We have a general interest in quantum and theoretical chemistry. The research described below focuses on solving the Schroedinger equation by using computer simulation methods.

The Schroedinger equation has locally singular potentials which have
to be canceled by the kinetic energy (electron-nuclear and electron-electron
cusps). Also, by virtue of the repulsion of like charges, each electron
influences the locations of all the others (electron correlation). These
effects must be reflected in the wavefunction, and it simply isn't efficient
to do this by taking combinations of Slater determinants with a finite
set of one-electron basis functions, as in the traditional

approaches. Furthermore, the traditional methods make huge computational
demands for systems containing a large number of electrons, necessitating
approximations or practical limits on the scale of the calculations.

Facilitated by the speed of modern computers, quantum Monte Carlo methods have been developed to complement the traditional methods. One statistically samples from a pre-specified, explicitly correlated wavefunction (depends explicitly upon the interelectronic distances) and thereby treats the various electron correlation effects explicitly. Other features of the exact wavefunction, such as the electron-electron and electron-nuclear cusps are also treated in a direct manner.

Our Monte Carlo research includes the following objectives::

accurate treatment of systems containing heavy atoms.

accurate computed physical properties other than the energy.

accurate estimation of the relativistic effects.

These efforts have a strong interdiscipinary flavour. Professor Rothstein has a cross appointment in the Department of Physics and can supervise students in either chemistry or physics.

At present our group consists of two undergraduate-level chemists: Ms. Heather Cuthbert and Mr. Jason Dwyer , and Mr. Martin Snajdr who is doing his MSc research in physics.

P. Langfelder, S.M. Rothstein, and J. Vrbik, "Diffusion Quantum Monte
Carlo Calculation of Nondifferential Properties for Atomic Ground States",
*J.
Chem. Phys.* **107**, 8525-8535 (1997).

S.M. Rothstein, "All-Electron Monte Carlo Calculations on Heavy Atom
Systems", in* Recent Advances in Quantum Monte Carlo Methods*, ed.
by W.A. Lester, Jr. (World Scientific, Singapore, 1997) pp 181-187

S.M. Rothstein, "Valence Hamiltonian for Quantum Monte Carlo: Dissociation
Energy of CuH", *Intern. J. Quantum Chem. * **60**, 803-808
(1996) and **61**, 153 (1997).

P. Belohorec, S.M. Rothstein, and J. Vrbik, "Infinitesimal Differential
Diffusion Quantum Monte Carlo Study of CuH Spectroscopic Constants", *J.
Chem. Phys.* **98**, 6401-6405 (1993).

H. Bueckert, S.M. Rothstein, and J. Vrbik, "Optimization of Quantum
Monte Carlo Wavefunctions using Analytical Derivatives", *Canad. J. Chem.***70**,
366-371 (1992).

H. Bueckert, S.M. Rothstein and J. Vrbik, "Relativistic Variational
Monte Carlo", *Chem. Phys. Lettr*. **190**, 413-416 (1992).

J. Vrbik, D.A. Legare, and S.M. Rothstein, "Infinitesimal Differential
Diffusion Quantum Monte Carlo, Diatomic Physical Properties",* J. Chem.
Phys*. **92**,1221-1227 (1990).

This page is: *http://chemiris.labs.brocku.ca/~chemweb/faculty/rothstein/*

Revised: July 5, 2000
*© copyright 1995 Brock University*