10.1021/acs.jpcb.6b06585.s001 Lorenzo Cupellini Lorenzo Cupellini Sandro Jurinovich Sandro Jurinovich Marco Campetella Marco Campetella Stefano Caprasecca Stefano Caprasecca Ciro A. Guido Ciro A. Guido Sharon M. Kelly Sharon M. Kelly Alastair T. Gardiner Alastair T. Gardiner Richard Cogdell Richard Cogdell Benedetta Mennucci Benedetta Mennucci An <i>Ab Initio</i> Description of the Excitonic Properties of LH2 and Their Temperature Dependence American Chemical Society 2016 excitation dynamics atomistic understanding crystal structure light-harvesting antenna room temperature spectroscopic properties alternative strategy photosyntehtic organisms ab initio X-ray crystallography excitonic properties Temperature Dependence spectroscopic observations LH 2 system LH 2 level explanation temperature dependence Excitonic Properties Ab Initio Description 2016-10-19 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/An_i_Ab_Initio_i_Description_of_the_Excitonic_Properties_of_LH2_and_Their_Temperature_Dependence/4123410 The spectroscopic properties of light-harvesting (LH) antennae in photosyntehtic organisms represent a fingerprint that is unique for each specific pigment–protein complex. Because of that, spectroscopic observations are generally combined with structural data from X-ray crystallography to obtain an indirect representation of the excitonic properties of the system. Here, an alternative strategy is presented which goes beyond this empirical approach and introduces an <i>ab initio</i> computational description of both structural and electronic properties and their dependence on the temperature. The strategy is applied to the peripheral light-harvesting antenna complex (LH2) present in purple bacteria. By comparing this model with the one based on the crystal structure, a detailed, molecular level explanation of the absorption and circular dichroism (CD) spectra and their temperature dependence is achieved. The agreement obtained with the experiments at both low and room temperature lays the groundwork for an atomistic understanding of the excitation dynamics in the LH2 system.