Recent Developments in the General Atomic and Molecular Electronic Structure System

A discussion of many of the recently implemented features of GAMESS (General Atomic and Molecular Electronic Structure System) and LibCChem (the C++ CPU/GPU library associated with GAMESS) is presented. These features include fragmentation methods such as the fragment molecular orbital, effective fragment potential and effective fragment molecular orbital methods, hybrid MPI/OpenMP approaches to Hartree-Fock, and resolution of the identity second order perturbation theory. Many new coupled cluster theory methods have been implemented in GAMESS, as have multiple levels of density functional/tight binding theory. The role of accelerators, especially graphical processing units, is discussed in the context of the new features of LibCChem, as it is the associated problem of power consumption as the power of computers increases dramatically. The process by which a complex program suite such as GAMESS is maintained and developed is considered. Future developments are briefly summarized

An Efficient Analytic Approach for Calculation of Multi-Dimensional Franck–Condon Factors and Associated Photoelectron Spectra

The implementation, optimization, and performance of a generalized analytic treatment of multidimensional Franck–Condon Factors (FCF) within the harmonic oscillator approximation and associated photoelectron spectra (PES) for N-dimensional systems, including consideration of Eckart conditions in the displacement minimization and Cartesian coordinate handedness for evaluation of the Duschinsky Effect, is carried out in this work. A new efficient strategy for algorithmic efficiency for high dimensional systems is introduced, and demonstrated for 3-, 15-, and 30-dimensional systems. Determination of the photoelectron spectra for H₂O⁺ (<i>B̃</i>²<i>B</i>₂), vinyl alcohol, and C₆H₆⁺ (<i>X̃</i>²<i>E</i>_1<i>g</i>) validates the capabilities with a high degree of accuracy with respect to experiment

On the origins of nonradiative excited state relaxation in aryl sulfoxides relevant to fluorescent chemosensing

We provide herein a mechanistic analysis of aryl sulfoxide excited state processes, inspired by our recent report of aryl sulfoxide based fluorescent chemosensors. The use of aryl sulfoxides as reporting elements in chemosensor development is a significant deviation from previous approaches, and thus warrants closer examination. We demonstrate that metal ion binding suppresses nonradiative excited state decay by blocking formation of a previously unrecognized charge transfer excited state, leading to fluorescence enhancement. This charge transfer state derives from the initially formed locally excited state followed by intramolecular charge transfer to form a sulfoxide radical cation/aryl radical anion pair. With the aid of computational studies, we map out ground and excited state potential energy surface details for aryl sulfoxides, and conclude that fluorescence enhancement is almost entirely the result of excited state effects. This work expands previous proposals that excited state pyramidal inversion is the major nonradiative decay pathway for aryl sulfoxides. We show that pyramidal inversion is indeed relevant, but that an additional and dominant nonradiative pathway must also exist. These conclusions have implications for the design of next generation sulfoxide based fluorescent chemosensors

Computation of host–guest binding free energies with a new quantum mechanics based mining minima algorithm

A new method called QM-VM2 is presented that efficiently combines statistical mechanics with quantum mechanical (QM) energy potentials in order to calculate noncovalent binding free energies of host–guest systems. QM-VM2 efficiently couples the use of semi-empirical QM (SEQM) energies and geometry optimizations with an underlying molecular mechanics (MM) based conformational search, to find low SEQM energy minima, and allows for processing of these minima at higher levels of ab initio QM theory. A progressive geometry optimization scheme is introduced as a means to increase conformational sampling efficiency. The newly implemented QM-VM2 is used to compute the binding free energies of the host molecule cucurbit[7]uril and a set of 15 guest molecules. The results are presented along with comparisons to experimentally determined binding affinities. For the full set of 15 host–guest complexes, which have a range of formal charges from +1 to +3, SEQM-VM2 based binding free energies show poor correlation with experiment, whereas for the ten +1 complexes only, a significant correlation (R2 = 0.8) is achieved. SEQM-VM2 generation of conformers followed by single-point ab initio QM calculations at the dispersion corrected restricted Hartree–Fock-D3(BJ) and TPSS-D3(BJ) levels of theory, as post-processing corrections, yields a reasonable correlation with experiment for the full set of host–guest complexes (R2 = 0.6 and R2 = 0.7, respectively) and an excellent correlation for the +1 formal charge set (R2 = 1.0 and R2 = 0.9, respectively), as long as a sufficiently large basis set (triple-zeta quality) is employed. The importance of the inclusion of configurational entropy, even at the MM level, for the achievement of good correlation with experiment was demonstrated by comparing the calculated ΔE values with experiment and finding a considerably poorer correlation with experiment than for the calculated free energy ΔE − TΔS. For the complete set of host–guest systems with the range of formal charges, it was observed that the deviation of the predicted binding free energy from experiment correlates somewhat with the net charge of the systems. This observation leads to a simple empirical interpolation scheme to improve the linear regression of the full set.This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Xu, Peng, Tosaporn Sattasathuchana, Emilie Guidez, Simon P. Webb, Kilinoelani Montgomery, Hussna Yasini, Iara FM Pedreira, and Mark S. Gordon. "Computation of host–guest binding free energies with a new quantum mechanics based mining minima algorithm." The Journal of Chemical Physics 154, no. 10 (2021): 104122, and may be found at DOI: 10.1063/5.0040759. Copyright 2022 Author(s). Posted with permission

Recent developments in the general atomic and molecular electronic structure system

A discussion of many of the recently implemented features of GAMESS (General Atomic and Molecular Electronic Structure System) and LibCChem (the C++ CPU/GPU library associated with GAMESS) is presented. These features include fragmentation methods such as the fragment molecular orbital, effective fragment potential and effective fragment molecular orbital methods, hybrid MPI/OpenMP approaches to Hartree–Fock, and resolution of the identity second order perturbation theory. Many new coupled cluster theory methods have been implemented in GAMESS, as have multiple levels of density functional/tight binding theory. The role of accelerators, especially graphical processing units, is discussed in the context of the new features of LibCChem, as it is the associated problem of power consumption as the power of computers increases dramatically. The process by which a complex program suite such as GAMESS is maintained and developed is considered. Future developments are briefly summarized.</p