15955
On the basis of a two - site diradical model with two electrons in two orbitals , the linear dependence of these excitation energies on the transfer integral , which is equivalent to the energy gap between the highest occupied ( HOMO ) and the lowest unoccupied ( LUMO ) molecular orbitals in the H u ckel theory , is found to be broken down in the high diradical character region due to an increase in electron correlation in the open - shell singlet ground state .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
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