def METHOD_NAME(self):
    """Custom guesses for environment variable PATH for CHARMM."""
    guesses = super(EB_CHARMM, self).METHOD_NAME()
    if self.toolchain.options.get('usempi', None):
        suffix = "_M"
    else:
        suffix = ""
    guesses.update({
        'PATH': ['exec/%s%s' % (self.arch, suffix)],
    })
    return guesses