Speeding Up Hartree–Fock in JuliaChem with Density Fitting

In this work, the density fitting (DF) approximation
is added to
the restricted Hartree–Fock (RHF) implementation in the JuliaChem
computational chemistry code. Utilizing a DF algorithm that uses symmetry
and integral screening, a significant reduction in time to compute
the Fock matrix is achieved. The symmetry and screening DF-RHF techniques
were adapted to be performed on graphics processing units (GPUs),
which are well suited to perform the matrix multiplications that comprise
the bulk of the Fock build time in DF-RHF. The JuliaChem DF-RHF GPU
algorithm employs a novel approach that automatically switches between
two DF-RHF algorithms depending on the number of basis functions in
the calculation. The JuliaChem GPU DF-RHF implementation demonstrates
up to 2× speedup for Fock build times compared to the existing
best-in-class GPU DF-RHF implementation by operating directly on screened
intermediate matrices. Due to the high portability of the Julia language
code, the JuliaChem CPU and GPU DF-RHF implementations could be benchmarked
on a variety of CPU and GPU architectures from multiple hardware vendors.