# Time-consuming frequency calculations with Q-chem

Hello, I am having trouble calculating frequency with Q-chem (JOBTYPE=freq). In most jobs, the calculation of frequencies by Q-chem takes much longer than other computational codes, and during this calculation, I encounter the following warning:

“Warning
Analytical derivatives of interest are not available.
A finite difference job could take a long time.”

Is there a specific keyword or method for resolving this problem?

If you could post an example input I can help.

But that warning has no way to be resolved, that warning is saying that with your interested method for the job type(in this case Hessian for frequency) are not available. Therefore Q-Chem defaults to using numerical derivatives and prints a warning.

So the reason the job may be taking a long time is that you are calculating a Hessian using numerical derivatives, and it may be by energy values. Which could take a long time depending on the size of the system.

Dear Pfmclaug.
Thank you for responding.
I have included a copy of my input below.
Furthermore, I must state that I performed this calculation using the b3lyp and m062x, but it still took a long time with the same warning. This is despite the fact that the same calculation is performed very quickly in other codes (Gaussian and ADF).
Can I use the frequency calculation methods from another code in Q-chem?

My input:
\$molecule
0 3
O 1.0687313 0.9343492 0.0484098
C -0.0163726 0.1440075 0.0063872
C -1.2824734 0.8368089 0.0183586
C 0.0278831 -1.2421923 -0.0445687
C -2.4718851 0.0474906 -0.0216207
C -1.1474643 -1.9755302 -0.0828820
H 0.9814175 -1.7549774 -0.0538967
C -2.3840139 -1.3182769 -0.0707659
H -3.4324373 0.5428485 -0.0122725
H -1.1080656 -3.0578879 -0.1217136
C 2.3440267 0.3726376 0.0325528
C 2.9723330 0.1000303 1.2384287
C 2.9783063 0.1802372 -1.1856524
C 4.2757669 -0.3853956 1.2182924
H 2.4473393 0.2734700 2.1719114
C 4.2814780 -0.3060359 -1.1911640
H 2.4582858 0.4153030 -2.1083725
C 4.9301782 -0.5895069 0.0071259
H 4.7806628 -0.6002103 2.1547841
H 4.7909651 -0.4589045 -2.1372892
H 5.9480079 -0.9661669 -0.0028767
Cl -3.8469110 -2.2772149 -0.1197229
N -1.2123082 2.1656114 0.0662466
N -2.6598381 2.7563878 0.0713592
N -2.8639412 3.8829204 0.1093377
\$end

\$rem
JOBTYPE freq
METHOD cam-b3lyp
BASIS 6-31G(d)
SPIN_FLIP true
CIS_STATE_DERIV = 2
CIS_N_ROOTS = 4
CIS_SINGLETS = true
CIS_TRIPLETS = false
SOLVENT_METHOD smd
SET_ITER 500
MAX_SCF_CYCLES 500
\$end

\$smx
solvent thf
\$end

@@@

\$molecule
\$end

\$rem
JOBTYPE ts
METHOD cam-b3lyp
BASIS 6-31G(d)
SPIN_FLIP true
CIS_STATE_DERIV = 2
CIS_N_ROOTS = 4
CIS_SINGLETS = true
CIS_TRIPLETS = false
GEOM_OPT_DMAX 100
GEOM_OPT_MAX_CYCLES 1500
SYMMETRY false
SYM_IGNORE true
SOLVENT_METHOD smd
SET_ITER 500
MAX_SCF_CYCLES 500
\$end

\$smx
solvent thf
\$end

@@@

\$molecule
\$end

\$rem
JOBTYPE freq
METHOD cam-b3lyp
BASIS 6-31G(d)
SPIN_FLIP true
CIS_STATE_DERIV = 2
CIS_N_ROOTS = 4
CIS_SINGLETS = true
CIS_TRIPLETS = false
SOLVENT_METHOD smd
SET_ITER 500
MAX_SCF_CYCLES 500
\$end

\$smx
solvent thf
\$end

@@@

\$molecule
\$end

\$rem
METHOD cam-b3lyp
BASIS GEN
PURECART 11
SPIN_FLIP true
CIS_STATE_DERIV = 2
CIS_N_ROOTS = 4
CIS_SINGLETS = true
CIS_TRIPLETS = false
SOLVENT_METHOD smd
SET_ITER 500
MAX_SCF_CYCLES 500
\$end

\$smx
solvent thf
\$end

\$basis
H 0
S 3 1.00
34.0613410 0.60251978D-02
5.1235746 0.45021094D-01
1.1646626 0.20189726
S 1 1.00
0.32723041 1.0000000
S 1 1.00
0.10307241 1.0000000
P 1 1.00
0.8000000 1.0000000

C 0
S 6 1.00
13575.3496820 0.22245814352D-03
2035.2333680 0.17232738252D-02
463.22562359 0.89255715314D-02
131.20019598 0.35727984502D-01
42.853015891 0.11076259931
15.584185766 0.24295627626
S 2 1.00
6.2067138508 0.41440263448
2.5764896527 0.23744968655
S 1 1.00
0.57696339419 1.0000000
S 1 1.00
0.22972831358 1.0000000
S 1 1.00
0.95164440028D-01 1.0000000
P 4 1.00
34.697232244 0.53333657805D-02
7.9582622826 0.35864109092D-01
2.3780826883 0.14215873329
0.81433208183 0.34270471845
P 1 1.00
0.28887547253 .46445822433
P 1 1.00
0.10056823671 .24955789874
D 1 1.00
1.09700000 1.0000000
D 1 1.00
0.31800000 1.0000000
F 1 1.00
0.76100000 1.0000000

N 0
S 6 1.00
19730.8006470 0.21887984991D-03
2957.8958745 0.16960708803D-02
673.22133595 0.87954603538D-02
190.68249494 0.35359382605D-01
62.295441898 0.11095789217
22.654161182 0.24982972552
S 2 1.00
8.9791477428 0.40623896148
3.6863002370 0.24338217176
S 1 1.00
0.84660076805 1.0000000
S 1 1.00
0.33647133771 1.0000000
S 1 1.00
0.13647653675 1.0000000
P 4 1.00
49.200380510 0.55552416751D-02
11.346790537 0.38052379723D-01
3.4273972411 0.14953671029
1.1785525134 0.34949305230
P 1 1.00
0.41642204972 .45843153697
P 1 1.00
0.14260826011 .24428771672
D 1 1.00
1.65400000 1.0000000
D 1 1.00
0.46900000 1.0000000
F 1 1.00
1.09300000 1.0000000

O 0
S 6 1.00
27032.3826310 0.21726302465D-03
4052.3871392 0.16838662199D-02
922.32722710 0.87395616265D-02
261.24070989 0.35239968808D-01
85.354641351 0.11153519115
31.035035245 0.25588953961
S 2 1.00
12.260860728 0.39768730901
4.9987076005 0.24627849430
S 1 1.00
1.1703108158 1.0000000
S 1 1.00
0.46474740994 1.0000000
S 1 1.00
0.18504536357 1.0000000
P 4 1.00
63.274954801 0.60685103418D-02
14.627049379 0.41912575824D-01
4.4501223456 0.16153841088
1.5275799647 0.35706951311
P 1 1.00
0.52935117943 .44794207502
P 1 1.00
0.17478421270 .24446069663
D 1 1.00
2.31400000 1.0000000
D 1 1.00
0.64500000 1.0000000
F 1 1.00
1.42800000 1.0000000

Cl 0
S 7 1.00
69507.9909450 0.54314897497D-03
10426.1568800 0.41990463961D-02
2373.2334061 0.21592141679D-01
671.56420071 0.84598850094D-01
218.41999790 0.24757249724
77.572249714 0.47016930228
28.888815277 0.37436370716
S 3 1.00
127.10527185 0.25182166603D-01
39.339582961 0.10786112456
7.6740679989 -0.27408821574
S 2 1.00
3.8745627630 1.3213875014
1.8385832573 0.68636955368
S 1 1.00
0.50229057542 1.0000000
S 1 1.00
0.17962723420 1.0000000
P 5 1.00
666.50423284 0.23632663836D-02
157.64241690 0.18879300374D-01
50.262520978 0.87206341273D-01
18.536078105 0.25285612970
7.2940532777 0.43507154820
P 1 1.00
2.9433248995 .35026513165
P 1 1.00
1.0404970818 1.0000000
P 1 1.00
0.38456415080 1.0000000
P 1 1.00
0.13069642732 1.0000000
D 2 1.00
4.61000000 0.20000000
1.01100000 1.00000000
D 1 1.00
0.339000000 1.0000000
F 1 1.00
0.706000000 1.0000000

\$end

Analytic Hessian is not available for spin-flip methods, so your calculation is using finite-difference as Peter suggests. (That’s what the large warning message set off in asterisks at the top of the Q-Chem output is telling you.) I have no idea if other codes have analytic Hessians. Comparison of timings to ADF is not straightforward because the representation of the orbitals is completely different (i.e., doesn’t use the same basis sets).

Dear John, Thank you very much! It’s just that this is an error even if no spin-flip methods are used (like below). Is it stated anywhere that Analytic Hessian is available for which methods?

## User input:

\$molecule
0 1
N -0.91535433 -0.01968504 0.00000000
N -2.00735433 -0.01968504 0.00000000
\$end

\$rem
JOBTYPE freq
METHOD cam-b3lyp
BASIS 6-31G(d)
SYMMETRY false
SYM_IGNORE true
SOLVENT_METHOD smd
SET_ITER 500
MAX_SCF_CYCLES 500
\$end

\$smx
solvent thf
\$end

That warning is still there because of the `solvent_method smd` which does not support TDDFT Analytic Hessian as observed in Table 11.2 in the Manual.

Peter, thank you for posting the link. These explanations solved my problem.