title: Benchmarking DFT and TD-DFT Functionals for the Ground and Excited States of Hydrogen-Rich Peptide Radicals.
abstract: We assess the pros and cons of a large panel of DFT exchange-correlation functionals for the prediction of the electronic structure of hydrogen-rich peptide radicals formed after electron attachment on a protonated peptide. Indeed, despite its importance in the understanding of the chemical changes associated with the reduction step, the question of the attachment site of an electron and, more generally, of the reduced species formed in the gas phase through electron-induced dissociation (ExD) processes in mass spectrometry is still a matter of debate. For hydrogen-rich peptide radicals in which several positive groups and low-lying π* orbitals can capture the incoming electron in ExD, inclusion of full Hartree-Fock exchange at long-range interelectronic distance is a prerequisite for an accurate description of the electronic states, thereby excluding several popular exchange-correlation functionals, e.g., B3LYP, M06-2X, or CAM-B3LYP. However, we show that this condition is not sufficient by comparing the results obtained with asymptotically correct range-separated hybrids (M11, LC-BLYP, LC-BPW91, ωB97, ωB97X, and ωB97X-D) and with reference CASSCF-MRCI and EOM-CCSD calculations. The attenuation parameter ω significantly tunes the spin density distribution and the excited states vertical energies. The investigated model structures, ranging from methylammonium to hexapeptide, allow us to obtain a description of the nature and energy of the electronic states, depending on (i) the presence of hydrogen bond(s) around the cationic site(s), (ii) the presence of π* molecular orbitals (MOs), and (iii) the selected DFT approach. It turns out that, in the present framework, LC-BLYP and ωB97 yields the most accurate results.
authors.affiliation: Laboratoire de Chimie Moléculaire, Département de Chimie, Ecole polytechnique and CNRS, 91128 Palaiseau cedex, France.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Riffet
authors.affiliation: Laboratoire CEISAM, UMR CNRS 6230, Université de Nantes , 2 rue de la Houssinière - BP 92208, 44322 Nantes cedex 3, France.|Institut Universitaire de France, 103 bd Saint-Michel, F-75005 Paris Cedex 05, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Jacquemin
authors.affiliation: Service de Chimie quantique et Photophysique, Université Libre de Bruxelles , CP160/09, 50 av. F.D. Roosevelt, 1050 Bruxelles, Belgium.
authors.forename: Emilie
authors.initials: E
authors.lastname: Cauët
authors.affiliation: Laboratoire de Chimie Moléculaire, Département de Chimie, Ecole polytechnique and CNRS, 91128 Palaiseau cedex, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Frison