Highly-accurate Energy,Structure,and Spectroscopy Properties Of Molecules With Multiple Sulfur Atom

The experimental laboratory-based investigations,as well as astronomical observations or technology applications,usually need to be supported and/or complemented by computer simulations.Among different theoretical models,ab initio quantum-mechanical computations represent a unique tool,in which atomic properties are described based on the same physical laws,independently of the type of molecular system in the investigation.Whether it is isolated molecules in the gas phase,biomolecules,or the condensed matter systems,all can be studied employing ab initio quantum-mechanics methods.In the current study,the interesting cases are represented by the systems with the disulfide bond and hydrogen polysulfides,since they play important roles in astronomy-and biology-related fields.In the past decades,experimental spectroscopy technologies have been applied to the investigation of a series of disulfide bond molecules and hydrogen polysulfides.These experimental data represent ideal references to test the accuracy of different quantum-mechanical models.In turn,theoretical methods are very helpful in predicting properties and parameters that have not been observed in experiments.Hence,in the current work,we employed a series of state-of-the-art quantummechanical methods including the Density Functional Theory(DFT),the M(?)llerPlesset(MP)perturbation theory,the Coupled-Cluster(CC)theory,as well as the composite scheme which combine several levels of theories together.These theoretical methods are applied to selected disulfide bond molecules and hydrogen polysulfides to reveal their highly accurate potential energy surface,equilibrium structure as well as spectroscopy parameters.The high accurate equilibrium structure(re)or semi-experimental equilibrium structure(reSE)for H₂S₂,(CH₃)₂S₂,(C₂H₅)₂S₂,and(C₃H₇)₂S₂ molecules are investigated in this study.Then,the theoretical benchmark studies of both basis sets and DFT methods are carried out for H₂S₂,(CH₃)₂S₂,(C₆H₅)2S2,and C₃H₅SS'C'3H'5 molecules,reporting that some functionals are very accurate in terms of equilibrium structures calculation.In the following,the electron localization function(ELF)and non-covalent interactions(NCI)analysis are applied for these disulfide bond molecules to further investigate the local nature of the chemical bonds.What's more,the conformational interconversion of the(C₃H₇)₂S₂ molecule and a suite of hydrogen polysulfides(H2Sn,with n = 2,3,4)are disclosed in the current work,these molecules have multiple conformers and complex potential energy surfaces(PES)due to torsions around the S-S or S-C bonds.At the end of this work,we also tested the accuracy of several theoretical models in calculating the rotational constants and vibrational frequencies of H₂S₂ and H₂S₃ molecules.The calculated results are compared with the obtainable experimental values,showing that the calculated rotational constants and vibrational frequencies from the current study agree with the corresponding experimental data within 0.1%.