{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,27]],"date-time":"2025-10-27T16:09:33Z","timestamp":1761581373627,"version":"build-2065373602"},"reference-count":116,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2015,12,4]],"date-time":"2015-12-04T00:00:00Z","timestamp":1449187200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Computation"],"abstract":"<jats:p>Ionization potentials (IPs) and electron affinities (EAs) are important quantities input into most models for calculating the open-circuit voltage (Voc) of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB) method with the third-order self-consistent charge (SCC) correction and the 3ob parameter set (the third-order DFTB (DFTB3) organic and biochemistry parameter set) against experiments (for smaller molecules) and against first-principles  GW (Green\u2019s function, G, times the screened potential, W) calculations (for larger molecules of interest in organic electronics) for the calculation of IPs and EAs. Since                                        GW calculations are relatively new for molecules of this size, we have also taken care to validate these calculations against experiments. As expected, DFTB is found to behave very much like density-functional theory (DFT), but with some loss of accuracy in predicting IPs and EAs. For small molecules, the best results were found with \u0394SCF (\u0394 self-consistent field) SCC-DFTB calculations for first IPs (good to \u00b1 0.649 eV). When considering several IPs of the same molecule, it is convenient to use the negative of the orbital energies (which we refer to as Koopmans\u2019 theorem (KT) IPs) as an indication of trends. Linear regression analysis shows that KT SCC-DFTB IPs are nearly as accurate as \u0394SCF SCC-DFTB eigenvalues (\u00b1 0.852 eV for first IPs, but \u00b1 0.706 eV for all of the IPs considered here) for small molecules. For larger molecules, SCC-DFTB was also the ideal choice with IP\/EA errors of \u00b1 0.489\/0.740 eV from \u0394SCF calculations and of \u00b1 0.326\/0.458 eV from (KT) orbital energies. Interestingly, the linear least squares fit for the KT IPs of the larger molecules also proves to have good predictive value for the lower energy KT IPs of smaller molecules, with significant deviations appearing only for IPs of 15\u201320 eV or larger. We believe that this quantitative analysis of errors in SCC-DFTB IPs and EAs may be of interest to other researchers interested in DFTB investigation of large and complex problems, such as those encountered in organic electronics.<\/jats:p>","DOI":"10.3390\/computation3040616","type":"journal-article","created":{"date-parts":[[2015,12,9]],"date-time":"2015-12-09T07:06:30Z","timestamp":1449644790000},"page":"616-656","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":19,"title":["Assessment of Density-Functional Tight-Binding Ionization Potentials and Electron Affinities of Molecules of Interest for Organic Solar Cells Against First-Principles GW Calculations"],"prefix":"10.3390","volume":"3","author":[{"given":"Ala","family":"Darghouth","sequence":"first","affiliation":[{"name":"D\u00e9partement de Chimie Mol\u00e9culaire (DCM, UMR CNRS\/UJF 5250), Institut de Chimie Mol\u00e9culaire de Grenoble (ICMG, FR2607), Universit\u00e9 Joseph Fourier (Grenoble I), 301 rue de la Chimie, BP 53, F-38041 Grenoble Cedex 9, France"},{"name":"Department of Chemistry, College of Science, University of Mosul, Mosul 41002, Iraq"}]},{"given":"Mark","family":"Casida","sequence":"additional","affiliation":[{"name":"D\u00e9partement de Chimie Mol\u00e9culaire (DCM, UMR CNRS\/UJF 5250), Institut de Chimie Mol\u00e9culaire de Grenoble (ICMG, FR2607), Universit\u00e9 Joseph Fourier (Grenoble I), 301 rue de la Chimie, BP 53, F-38041 Grenoble Cedex 9, France"}]},{"given":"Walid","family":"Taouali","sequence":"additional","affiliation":[{"name":"Unit\u00e9 de Recherche: Mat\u00e9riaux Nouveaux et Dispositifs \u00c9lectroniques Organiques (UR 11ES55), Facult\u00e9 des Sciences de Monastir, Universit\u00e9 de Monastir, 5000 Monastir, Tunisia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5978-4637","authenticated-orcid":false,"given":"Kamel","family":"Alimi","sequence":"additional","affiliation":[{"name":"Unit\u00e9 de Recherche: Mat\u00e9riaux Nouveaux et Dispositifs \u00c9lectroniques Organiques (UR 11ES55), Facult\u00e9 des Sciences de Monastir, Universit\u00e9 de Monastir, 5000 Monastir, Tunisia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8774-9529","authenticated-orcid":false,"given":"Mathias","family":"Ljungberg","sequence":"additional","affiliation":[{"name":"Department of Physics, Phillips-University Marburg, Renthof 5, 35032 Marburg, Germany"},{"name":"Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, E-20018 San Sebasti\u00e1n, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5461-2278","authenticated-orcid":false,"given":"Peter","family":"Koval","sequence":"additional","affiliation":[{"name":"Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, E-20018 San Sebasti\u00e1n, Spain"},{"name":"Centro de F\u00edsica de Materiales CFM-MPC, Centro Mixto CSIC-UPV\/EHU, Paseo Manuel de Lardizabal 5, E-20018 San Sebasti\u00e1n, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6860-8790","authenticated-orcid":false,"given":"Daniel","family":"S\u00e1nchez-Portal","sequence":"additional","affiliation":[{"name":"Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, E-20018 San Sebasti\u00e1n, Spain"},{"name":"Centro de F\u00edsica de Materiales CFM-MPC, Centro Mixto CSIC-UPV\/EHU, Paseo Manuel de Lardizabal 5, E-20018 San Sebasti\u00e1n, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4885-6938","authenticated-orcid":false,"given":"Dietrich","family":"Foerster","sequence":"additional","affiliation":[{"name":"CPMOH\/LOMA, Universit\u00e9 de Bordeaux 1, 351 Cours de la Liberation, 33405 Talence, France"}]}],"member":"1968","published-online":{"date-parts":[[2015,12,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Sze, S.M., and Ng, K.K. 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