Molcas Forum

ordinaryboy

Member

Registered: 2017-12-15

Posts: 1

Problem with choosing the right active space

Hello!

Right now I'm trying to investigate the 2 lowest lying excited states in octatetraene by distorting the equilibrium geometry. but there's a problem within choosing the right active space for the calculation. I've tried 4 different active spaces for this calculation but none of them are seemingly appropriate and sufficient to solve the problem at some distortion

Here are the active spaces that I've already tried.

Orbital	Energy [Hartree]	               Symmetry	              (8,8)	    (8,12)	    (10,10)	   (12,12)
24			-0.5077			Bu (σ)			c		c		c		a
25			-0.4964			Ag (σ)			c		c		a		a
26			-0.4774			Au (π)			a		a		a		a
27			-0.4317			Bg (π)			a		a		a		a
28			-0.3612			Au (π)			a		a		a		a
29			-0.2740			Bg (π)			a		a		a		a
30			0.0663			Au (π)			a		a		a		a
31			0.1467			Bu (σ)			i		i		i		a
32			0.1590			Bg (π)			a		a		a		a
33			0.1594			Ag (σ)			i		i		a		a
34			0.1612			Bu (σ)			i		i		i		i
35			0.1736			Ag (σ)			i		i		i		i
36			0.1777			Ag (σ)			i		i		i		i
37			0.2035			Bu (σ)			i		i		i		i
38			0.2111			Bu (σ)			i		i		i		i
39			0.2145			Bg (π)			a		a		a		a
40			0.2164			Au (π)			a		a		a		a
41			0.2299			Ag (σ)			i		i		i		i
42			0.2585			Ag (σ)			i		i		i		i
43			0.2704			Bu (σ)			i		i		i		i
44			0.3174			Bu (σ)			i		i		i		i
45			0.3590			Ag (σ)			i		i		i		i
46			0.3623			Ag (σ)			i		i		i		i
47			0.4120			Bu (σ)			i		i		i		i
48			0.4216			Au (π)			i		a		i		i
49			0.4274			Ag (σ)			i		i		i		i
50			0.4314			Bu (σ)			i		i		i		i
51			0.4419			Bg (π)			i		a		i		i
52			0.4543			Bu (σ)			i		i		i		i
53			0.4576			Ag (σ)			i		i		i		i
54			0.4625			Bu (σ)			i		i		i		i
55			0.4775			Au (π)			i		a		i		i
56			0.4867			Ag (σ)			i		i		i		i
57			0.4931			Ag (σ)			i		i		i		i
58			0.5210			Bu (σ)			i		i		i		i
59			0.5275			Bg (π)			i		a		i		i

I've defined c, a, and i as closed, active, and inactive respectively..

can someone please help me or give me suggestions which active space I should choose so that I can solve this problem? I'd be very thankful

p.s: I'm still new both in MOLCAS and in this forum. so I'm so sorry if I posted this in the wrong section