  We present an efficient real space formalism for hybrid exchange-correlation
functionals in generalized Kohn-Sham density functional theory (DFT). In
particular, we develop an efficient representation for any function of the real
space finite-difference Laplacian matrix by leveraging its Kronecker product
structure, thereby enabling the time to solution of associated linear systems
to be highly competitive with the fast Fourier transform scheme, while not
imposing any restrictions on the boundary conditions. We implement this
formalism for both the unscreened and range-separated variants of hybrid
functionals. We verify its accuracy and efficiency through comparisons with
established planewave codes for isolated as well as bulk systems. In
particular, we demonstrate up to an order-of-magnitude speedup in time to
solution for the real space method. We also apply the framework to study the
structure of liquid water using ab initio molecular dynamics, where we find
good agreement with literature. Overall, the current formalism provides an
avenue for efficient real space DFT calculations with hybrid density
functionals.
