Table 5. Singlet–triplet energy gaps (kcal mol^–1) for WFP-3 partitions ^a .

Acene	(n,m)	GASSCF		GASPT2		tPBE (GAS-PDFT)		Literature values b
		Vert.	Ad.	Vert.	Ad.	Vert.	Ad.	Vert. c	Ad. d
Naphthalene	(10,10)	72.8	63.4	74.5	65.7	74.9	64.7	76.0	64.4
Anthracene	(14,14)	57.9	49.0	54.1	46.6	50.4	43.1	56.8	46.2
Tetracene	(18,18)	45.5	37.8	40.4	33.9	34.7	28.8	40.4	34.1
Pentacene	(22,22)	34.0	27.1			25.0	20.5	31.3	24.3
Hexacene	(26,26)	25.6	20.4			17.3	15.0	22.8	18.7
Heptacene	(30,30)	16.9	14.5			10.6	10.0	18.1	13.9
Octacene	(34,34)	12.4	10.7			5.4	6.4	13.4	11.5
Nonacene	(38,38)	9.8	8.4			4.4	5.0	10.7	10.4
Decacene	(42,42)	8.2	6.5			3.7	5.1	8.1	9.0
Undecacene	(46,46)	7.8	5.6			1.6	3.1	7.1	9.4
MUD e		1.9	2.2			5.7	4.1

^aGeometries are optimized using B3LYP/6-31G(d,p) level of theory. CASSCF, GASPT2 and tPBE calculations are performed using 6-31+G(d,p) basis set.

^bHighest-level available literature estimates.

^cCCSD(T)/cc-pV∞Z from ref. 21.

^dAverage adiabatic gaps from Table 1.

^eMean unsigned deviation.