AI Article Synopsis
- Understanding the significance of noncovalent interactions has led to a focus on identifying and analyzing stationary points (SP) in weakly bound oligomers for computational chemistry.
- A new algorithm called oligoCGO allows for efficient geometry optimization and vibrational analysis of oligomers, which can vary in structure and complexity.
- The implementation of two residual gradient correction (RGC) schemes addresses issues caused by nonzero forces during vibration analysis, significantly improving accuracy and yielding results consistent with unconstrained stationary points.
Article Abstract
Following the full realization of the importance of noncovalent interactions, finding and characterizing stationary points (SP), of various order, for weakly bound oligomers have become important tasks for computational chemists. An efficient algorithm and an associated computer code, called oligoCGO, are described, facilitating constrained geometry optimization of oligomers of arbitrary structure and complexity and normal-mode vibrational analysis at nonstationary geometries. To minimize the adverse effects of nonzero forces on harmonic vibrational analyses at constrained stationary points (cSP), two residual gradient correction (RGC) schemes are proposed. RGC, for which a rigorous justification is given, is based on ignoring the remaining forces in internal-coordinate space. RGC modifies the geometry of the cSP in a single Newton step and recalculates the Cartesian Hessian at this updated geometry. As demonstrated by 10 examples related to the water-water, water-methane, and methane-methane dimers as well as the methane trimer, without RGC the harmonic analysis of cSPs may result in even qualitatively incorrect results when compared to reference values obtained at the nearby unconstrained SPs (uSP). Both RGC protocols work exceedingly well, and the corrected harmonic wavenumbers of the cSPs are very close to their uSP counterparts.
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