I would like to get the overtones and the combination tones, but I can’t get them by anharmonic calculation. if I use Gaussian, I think I can calculate the overtones and the combination tones by anharmonic calculation, but in Q-Chem, how should I calculate them?

Any advice you can give us would be greatly appreciated.

The following is the actual input file used in the calculation.

$molecule

0 1

C -4.3555400 0.6876800 0.0030300

C -3.4738600 -0.5508400 -0.0085800

H -4.1530300 1.3221800 -0.8657400

H -4.1873200 1.2799600 0.9081500

H -5.4116000 0.4014400 -0.0239900

C -1.9916500 -0.1828600 0.0125000

H -3.6972700 -1.1432100 -0.9035200

H -3.7164100 -1.1730100 0.8608500

C -1.1101600 -1.4215700 0.0168400

H -1.7692300 0.4199200 0.9006700

H -1.7479400 0.4290500 -0.8639100

H -1.3002400 -2.0346600 0.9036400

H -0.0538300 -1.1350800 0.0222500

H -1.2912400 -2.0356600 -0.8710600

$end

$rem

METHOD b3lyp

BASIS 6-31G(d)

UNRESTRICTED 1

SCF_ALGORITHM = diis_gdm

MAX_DIIS_CYCLES = 1

SCF_GUESS = gwh

SCF_GUESS_MIX = 2

MAX_SCF_CYCLES 300

JOBTYPE opt

GEOM_OPT_DMAX 50

GEOM_OPT_MAX_CYCLES 1000

GEOM_OPT_CHARAC TRUE

SYMMETRY false

SYM_IGNORE true

integral_symmetry false

point_group_symmetry False

$end

@@@

$molecule

read

$end

$rem

METHOD b3lyp

BASIS 6-31g(d)

UNRESTRICTED 1

SCF_ALGORITHM = diis_gdm

MAX_DIIS_CYCLES = 1

SCF_GUESS = read

SCF_GUESS_MIX = 2

MAX_SCF_CYCLES 300

JOBTYPE freq

ANHAR TRUE

MODE_COUPLING 3

SYMMETRY false

SYM_IGNORE true

integral_symmetry false

point_group_symmetry False

$end