TDA with RSH giving negative triplet excitation

Questions
#1

Hello,
I am trying to obtain the singlet and triplet excitation energies for some molecules using the LCwPBE functional, with TDA. But I am actually getting the first triplet excitation with a negative value. What should I do?
Here is the input for your reference:

$comment
B_B_O
$end

$molecule
0 1
C -3.62650271490383 1.84809387627588 -0.20031656213029
C -2.64494069627883 0.80030371330622 -0.08162422772159
C -3.09391738265105 -0.54955436924551 0.05245182734149
C -4.46254990461043 -0.80368078435983 0.06314441793440
C -5.43893151762219 0.24674346719975 -0.05638036624317
C -4.99155270557869 1.58326746812945 -0.18868134819704
H -3.28702959644124 2.88664438540846 -0.30394402913536
H -2.35083324275376 -1.35331395805396 0.14344158701062
H -5.71697231591678 2.40462920549294 -0.28155352507590
H -4.69287976475051 -2.92558712482248 0.27819033350270
C -6.50714977773098 -1.79251485989195 0.14082128849821
C -7.56916632380000 -2.71094900582880 0.22247492020827
C -8.87183418711502 -2.19957287166716 0.15365683302839
C -9.12036185562526 -0.81069667829129 0.00713195615462
C -8.06395620599324 0.10100657969699 -0.07386140307076
C -6.73715449439281 -0.38137351978382 -0.00732659778693
H -7.38709794106071 -3.78948231504478 0.33566398598005
H -9.72228355393836 -2.89453382931922 0.21477345559173
H -10.15817247303870 -0.45160493118630 -0.04298811965658
H -8.25947890261030 1.17722994523906 -0.18811797901953
N -5.13866914349988 -2.01511477792599 0.18009201468675
C 3.11295779911888 2.32598459388954 -0.18885586252162
C 2.55109930417773 0.98495320653462 -0.05955917289506
C 1.17156686088761 0.89607101594266 -0.05814102924566
C 0.72008448755898 2.38464647248100 -0.20867341196515
C -1.22490882475195 1.06051449874251 -0.09360532621292
C -0.65663575819545 2.40943035271198 -0.22269063522767
H -1.24674894762253 3.33329237884800 -0.31920926278574
C 4.51090775915446 2.12524575246898 -0.16286754731462
C 4.73798238038922 0.74192552179673 -0.02607657321404
H 5.31133428848113 2.87130403440627 -0.23280085207310
C 5.97608043399304 0.05380505971443 0.04637083264142
C 6.22404824855486 -1.30149341693661 0.18030662069639
H 6.87847916817281 0.68249877617629 -0.01196300429076
C 5.22365630683594 -2.31392536166448 0.27670365049823
C 7.66559419718402 -1.70879656244673 0.22503103488005
N 4.43439421754876 -3.18636680640678 0.36045412283851
O 8.60719757883900 -0.92805352222971 0.15139322571677
O 7.81365151738357 -3.05368556239202 0.35800529304992
H 8.78718620624828 -3.20169704061255 0.37638767673721
H -0.13807650798141 -1.18028169846188 0.13875780994923
B 1.93973716790025 3.33358719352677 -0.29426288674738
H 1.97116436517001 4.53647496472876 -0.41233586348121
B -0.05107044808928 0.02074461705129 0.01986763010933
O 3.54155289935468 0.03598891680328 0.03823106895776
$end

$rem
SCF_CONVERGENCE 6
MAX_SCF_CYCLES 100
EXCHANGE gen
LRC_DFT = true
omega = 219
CIS_N_ROOTS 10
CIS_SINGLETS true
CIS_TRIPLETS true
RPA FALSE
BASIS def2-TZVPD
XC_GRID = 000099000590
MEM_TOTAL 2000000
THRESH 14
SYM_IGNORE TRUE
SYMMETRY FALSE
$end

$xc_functional
C PBE 1.00
X wPBE 1.00
$end

#2

Probably an instability in the reference state. Try a stability analysis (INTERNAL_STABILITY = TRUE).

#3

Hi John, I tried using this “INTERNAL_STABILITY = TRUE”, but still obtained a negative triplet excitation energy.

#4

What did the stability analysis say? If the solution is unstable, that code is set up to perturb the MOs in the direction of the downward curvature and leave them on disk, so that a subsequent job can read in the perturbed MOs (SCF_GUESS = READ) and try to find a stable solution.

#5

I went ahead and ran this. (Side note: for TDDFT or other calculations that require the wave function and not just the energy, we set SCF_CONVERGENCE = 8 by default so you’re loosening the convergence. Also, PBE doesn’t require a grid that’s nearly so dense; the default works just fine. Neither of those choices affects the specific issue at hand, however.)

What this is telling you is that the triplet state is slightly lower in energy than the singlet state, at this geometry and for this particular functional and basis set.

#6

here is what i got in the output

===================================================
Beginning Test for Internal Stability

generating davidson guess vectors based on koopmans excitations
1 8.55e-01 00000 Davidson Iteration
2 2.63e-01 00000 Davidson Iteration
3 2.31e-01 00000 Davidson Iteration
4 1.42e-01 00000 Davidson Iteration
5 8.69e-02 00000 Davidson Iteration
6 4.95e-02 00000 Davidson Iteration
7 4.36e-02 00000 Davidson Iteration
8 3.50e-02 00000 Davidson Iteration
9 1.55e-02 00000 Davidson Iteration
10 7.57e-03 00000 Davidson Iteration
11 4.54e-03 00000 Davidson Iteration
12 2.06e-03 00000 Davidson Iteration
13 8.45e-04 00000 Davidson Iteration
14 5.02e-04 00000 Davidson Iteration
15 2.01e-04 00000 Davidson Iteration
16 7.49e-05 00000 Davidson Iteration
17 1.76e-03 00000 Davidson Iteration
18 1.05e-03 00000 Davidson Iteration
19 4.90e-04 00000 Davidson Iteration
20 3.56e-04 00000 Davidson Iteration
21 2.28e-04 00000 Davidson Iteration
22 1.19e-04 00000 Davidson Iteration
23 7.81e-05 00000 Davidson Converged
converged_eigenvalues
0.1767
0.3162
Threshold for negative eigenvalues: -1.0e-05
solution was a local minimum (stable)

End Test for Internal Stability