3 research outputs found
Projector-Based Embedding Eliminates Density Functional Dependence for QM/MM Calculations of Reactions in Enzymes and Solution
Combined
quantum mechanics/molecular mechanics (QM/MM) methods
are increasingly widely utilized in studies of reactions in enzymes
and other large systems. Here, we apply a range of QM/MM methods to
investigate the Claisen rearrangement of chorismate to prephenate,
in solution, and in the enzyme chorismate mutase. Using projector-based
embedding in a QM/MM framework, we apply treatments up to the CCSDÂ(T)
level. We test a range of density functional QM/MM methods and QM
region sizes. The results show that the calculated reaction energetics
are significantly more sensitive to the choice of density functional
than they are to the size of the QM region in these systems. Projector-based
embedding of a wave function method in DFT reduced the 13 kcal/mol
spread in barrier heights calculated at the DFT/MM level to a spread
of just 0.3 kcal/mol, essentially eliminating dependence on the functional.
Projector-based embedding of correlated ab initio methods provides a practical method for achieving high accuracy
for energy profiles derived from DFT and DFT/MM calculations for reactions
in condensed phases
Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package
This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design