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# 2.8.2 GPU-accelerated Q-Chem with BrianQC

(February 4, 2022)

Starting with version 5.0, the core parts of Q-Chem calculations can be accelerated using the BrianQC GPU module. It does so by providing routines for computing all components of the Fock matrix (Eq. (4.18)): the core Hamiltonian, Coulomb, exchange, and exchange-correlation (Eq. (5.9)) integrals, along with their first derivatives and the most time-consuming parts of their second derivatives. This can lead to significant speedups when computing Hartree-Fock and density functional theory energies, gradients, vibrational frequencies, and other calculations requiring these quantities. Range-separated hybrid density functionals, where the exchange contribution is split into two terms (Eq. (5.12)), are also supported.

In order to invoke BrianQC, pass the -gpu flag when starting Q-Chem. Because BrianQC does not accelerate all parts of Q-Chem calculations, and GPU acceleration works transparently with OpenMP threading, it is still important to parallelize the remaining parts of a calculation using OpenMP threading.

qchem -gpu -nt nthreads infile outfile


Requirements for using BrianQC are:

• A basis set with $g$ angular momentum or lower functions