Citation: Martin, E.; Amiehe Essomba, I.B.; Ishisone, K.; Boero, M.; Ori, G.; Massobrio, C. Impact of Dispersion Force Schemes on Liquid Systems: Comparing Efficiency and Drawbacks for Well-Targeted Test Cases. Molecules 2022, 27, 9034. https://doi.org/10.3390/ molecules27249034 Academic Editor: Benedito José Costa Cabral Received: 14 November 2022 Accepted: 13 December 2022 Published: 18 December 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). molecules Article Impact of Dispersion Force Schemes on Liquid Systems: Comparing Efficiency and Drawbacks for Well-Targeted Test Cases Evelyne Martin 1 , Iréné Bérenger Amiehe Essomba 2 , Kana Ishisone 2 , Mauro Boero 2 , Guido Ori 2 and Carlo Massobrio 2, * 1 Laboratoire ICube, Université de Strasbourg, CNRS, UMR 7357, F-67037 Strasbourg, France 2 Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS, F-67034 Strasbourg, France * Correspondence: carlo.massobrio@ipcms.unistra.fr Abstract: First-principles molecular dynamics (FPMD) calculations were performed on liquid GeSe 4 with the aim of inferring the impact of dispersion (van der Waals, vdW) forces on the structural properties. Different expressions for the dispersion forces were employed, allowing us to draw conclusions on their performances in a comparative fashion. These results supersede previous FPMD calculations obtained in smaller systems and shorter time trajectories by providing data of unprecedented accuracy. We obtained a substantial agreement with experiments for the structure factor regardless of the vdW scheme employed. This objective was achieved by using (in addition to FPMD with no dispersion forces) a selection of vdW schemes available within density functional theory. The first two are due to Grimme, D2 and D3, and the third one is devised within the so-called maximally localized Wannier functions approach (MLWF). D3 results feature a sizeable disagreement in real space with D2 and MLWF in terms of the partial and total pair correlation functions as well as the coordination numbers. More strikingly, total and partial structure factors calculated with D3 exhibit an unexpected sharp increase at low k. This peculiarity goes along with large void regions within the network, standing for a phase separation of indecipherable physical meaning. In view of these findings, further evidence of unconventional structural properties found by employing D3 is presented by relying on results obtained for a complex ionic liquid supported on a solid surface. The novelty of our study is multifold: new, reliable FPMD data for a prototypical disordered network system, convincing agreement with experimental data and assessment of the impact of dispersion forces, with emphasis on the intriguing behavior of one specific recipe and the discovery of common structural features shared by drastically dissimilar physical systems when the D3 vdW scheme is employed. Keywords: dispersion forces; first-principles molecular dynamics; chalcogenides; disordered networks; liquid and glassy systems; density functional theory 1. Introduction Disordered systems can play a benchmark role in assessing the sensitivity of structural properties to the inclusion of dispersion forces (van der Waals, vdW hereafter) within the Kohn–Sham formulation of the density functional theory (DFT) [1]. By focusing on the family of chalcogenides, it is worth starting by quoting the seminal paper devoted to liquid Ge 15 Te 85 , in which it was proposed that more realistic pair correlation functions and struc- ture factors could be achieved by including vdW corrections [2]. Similar considerations were also developed later for liquid and amorphous GeTe [3,4]. However, it should be recognized that, despite their intrinsic validity, these contributions were more instrumental in opening a lively debate on the need of adding vdW corrections than in assessing their quantitative importance to improve the cohesive properties of disordered chalcogenides. Molecules 2022, 27, 9034. https://doi.org/10.3390/molecules27249034 https://www.mdpi.com/journal/molecules