The optimized structure was verified to be originated from a minimum without imaginary frequencies.įor our Mol-Instincts and/or ChemRTP users to be more efficient in accessing the required data and information, we are publishing the webpages providing various properties of pure chemical substances that may be readily found by Google search. Geometry optimization, frequency calculation, and the RI-MP2 energy correction have been performed using the DFT-B3LYP functional with 6-31G* basis set. The conformer with the lowest potential energy was then used as the starting structure for the quantum mechanical calculations. Subsequently, a simple potential energy calculation based on the MMFF94s force field proposed by Halgren, was carried out for each and every conformer. Depending on the number of the single bonds in the target substance, up to tens of thousands of conformers have been automatically generated. To obtain a good starting structure, the 3D structure generated by the structure generation engine was processed by a detailed conformer analysis in case the target chemical substance includes single bond(s). The 3D structure generation engine automatically generates all the possible isomers based on the atoms and their numbers provided by the user.Ī great effort has been made to secure a “good” starting structure since obtaining a reliable optimized geometry without imaginary frequencies depends severely on the starting geometry. The initial 3D structures of the chemical substances were generated by making use of a structure generation engine developed in-house. On the basis of the analysis of prediction accuracy of the various properties (including entropy, dipole moment, frequency, heat capacity, magnetic susceptibility, polarizability, radius of gyration, van der Waals area, and van der Waals volume), the DFT-B3LYP functional with 6-31G* basis set were found to be the optimal combination, which supplies a decent accuracy as well as a reasonable computation time. Prior to performing the actual quantum calculation, dozens of thousands of test calculations were carried out to determine an optimal combination of the methods (e.g., Hartree-Fock, Density Function Theory DFT, etc.) and basis sets (e.g., STO-3G, 6-31G*, etc.). The IR spectra have been determined through quantum mechanical calculations which are carefully tuned by using an optimal calculation method, basis set, and the starting structure of the chemical substance.
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