Dear Q-Chem community,
I’m new to Q-Chem and working on a system with two identical monomers separated by 20 Å. I’ve ensured that the ground-state calculations show degenerate energies for orbitals localized on each monomer. Now, I want to modify the orbital occupancy by transferring one electron from the HOMO on one monomer to the LUMO on the other (hence the charge of each monomer isn’t neutral anymore).
I tried to use the $swap_occupied_virtual feature by applying it only to the alpha electrons as follows:
$molecule
0 1
O -0.2341000 -2.0616800 1.5520400
O -6.2766000 1.5508000 -1.4368900
O -5.2904700 -2.1657900 1.0047900
N -5.7678900 -0.3078200 -0.2092700
C -1.6572700 0.6890800 -0.3489500
C -3.9890500 1.1869900 -0.9413700
C -3.0403700 0.3596900 -0.3055500
C -0.7178100 -0.1576600 0.2941600
C -2.5403000 -1.6250300 0.9862700
H -2.9304900 -2.5140200 1.4988000
C -3.4571300 -0.8005500 0.3687000
C -1.2769800 1.8523400 -1.0559500
H -0.2094400 2.1020300 -1.1152900
C -3.5831400 2.3205900 -1.6156700
H -4.3550800 2.9341700 -2.0979400
C -1.1731600 -1.3061000 0.9526600
C -5.4196300 0.8565400 -0.9004400
C -2.2196300 2.6471500 -1.6734000
H -1.9004300 3.5433800 -2.2198600
C -4.8779500 -1.1633100 0.4287400
C -0.6657400 -3.2197000 2.2216000
H -1.3656500 -2.9759400 3.0466800
H 0.2398300 -3.6891700 2.6370300
H -1.1634500 -3.9307300 1.5306900
C -7.1621800 -0.6701400 -0.1435400
H -7.3171500 -1.6643500 -0.5975400
H -7.4733700 -0.6959200 0.8798800
H -7.7381600 0.0540800 -0.6808000
H 0.2885700 0.0702000 0.2767200
H 20.2094500 -2.1020300 -1.1152900
C 23.9890600 -1.1869900 -0.9413700
C 25.4196400 -0.8565400 -0.9004300
H 19.7601100 3.6891400 2.6370200
O 26.2766100 -1.5508000 -1.4368800
C 21.2769900 -1.8523400 -1.0559500
C 22.2196400 -2.6471500 -1.6734000
H 21.9004400 -3.5433800 -2.2198500
C 23.5831500 -2.3205900 -1.6156700
H 24.3550900 -2.9341700 -2.0979400
O 20.2340900 2.0616800 1.5520400
O 25.2904700 2.1658000 1.0048000
N 25.7679000 0.3078200 -0.2092700
C 20.7178200 0.1576600 0.2941600
C 23.4571300 0.8005500 0.3687000
C 23.0403700 -0.3596900 -0.3055500
C 21.1731600 1.3061000 0.9526600
C 21.6572800 -0.6890800 -0.3489500
C 24.8779500 1.1633100 0.4287400
C 22.5403000 1.6250300 0.9862700
H 22.9304900 2.5140200 1.4988000
C 20.6656900 3.2196900 2.2216100
H 21.3656000 2.9759500 3.0467000
H 21.1633900 3.9307400 1.5307000
C 27.1621900 0.6701500 -0.1435300
H 27.3171600 1.6643600 -0.5975400
H 27.4733700 0.6959400 0.8799000
H 27.7381800 -0.0540700 -0.6807800
H 19.7114400 -0.0702100 0.2767200
$end
$rem
BASIS = 6-31G*
GUI = 2
METHOD = B3LYP
$end
@@@
$molecule
read
$end
$rem
BASIS = 6-31G*
GUI = 2
JOB_TYPE = SP
METHOD = B3LYP
SCF_CONVERGENCE = 8
SCF_GUESS = READ
$end
$swap_occupied_virtual
alpha 126 127
$end
Where alpha 126 is the HOMO, localized on the left monomer and alpha 127 is the LUMO, localized on the right monomer.
Inspecting the output, I found out that Q-Chem essentially just swapped the orbitals 127 with 128 (which was localized on the left monomer, as 126, but with the same shape and energy of the 127), while the 126 orbital has the same energy and shape as before. Moreover, the charge of the monomers remained neutral.
My goal is to freeze the involved orbitals and observe an actual electron transfer resulting in non-neutral monomers. Any advice on how to achieve this would be greatly appreciated. Additionally, if you know of any resources that explain the swapping feature in more detail beyond the usual manual, I would love to hear about them.
Thanks in advance for your help!
Best,
Arianna Cantarella, University of Parma.
P.S. I also tried constrained DFT to enforce charge separation but couldn’t get the calculations to converge, also enforcing the convergence with different methods.