# Introduction

In the olden days, before the light of dawn, there was a man named Krüger.

(Fonzé 1995)

# Computational Details

All calculations were done in the Dalton(Aidas 2013) program.

# Theory

The transition density matrix between the groundstate $$i$$ and the excited state $$a$$ is $\rho^T_{J,ia}(r) = \rho^g_{J,i}(r) - \rho^e_{J,a}(r)$

The coupling between the excited state $$i$$ on molecule $$I$$ and excited state $$j$$ on molecule $$J$$ is $V_{IJ} = \iint \mathrm{d}r \, \mathrm{d}r' \frac{\rho^T_{I,ia}(r)\rho^T_{J,jb}(r')}{|r-r'|}$