def assign_scheme(self, scheme):
    if (scheme is None):
        return 'chem'
    else:
        scheme = str(scheme)
    if (scheme.lower() in ['mulliken', 'chem', 'c', '1122']):
        return 'chem'
    elif (scheme.lower() in ['dirac', 'phys', 'p', '1212']):
        return 'phys'
    elif (scheme.lower() in ['openfermion', 'of', 'o', '1221']):
        return 'of'
    else:
        raise TequilaException('Unknown two-body tensor scheme {}. Supported are dirac, mulliken, and openfermion'.format(scheme))
def assign_scheme(self, scheme):
    if (scheme is None):
        return 'chem'
    else:
        scheme = str(scheme)
    if (scheme.lower() in ['mulliken', 'chem', 'c', '1122']):
        return 'chem'
    elif (scheme.lower() in ['dirac', 'phys', 'p', '1212']):
        return 'phys'
    elif (scheme.lower() in ['openfermion', 'of', 'o', '1221']):
        return 'of'
    else:
        raise TequilaException('Unknown two-body tensor scheme {}. Supported are dirac, mulliken, and openfermion'.format(scheme))