The FORTRAN 90 code and sample methane potential can be downloaded by clicking the link below. The primary citation for this code is the Wang et al. reference below. 

References. 

Wang et al. J. Chem. Phys. 2008, 128, 224314. Our code 

Anderson, J. Chem.Phys.1975,63, 1499. Theory and methodology

Anderson,.J. Chem. Phys.1976,65, 4121. Theory and methodology

Kosztin, I.; Faber, B.; Schulten, K. Am. J. Phys.1996,64, 633.  Pedagogical 

dmc_CH4