  Reliable theoretical predictions of noncovalent interaction energies, which
are important e.g. in drug-design and hydrogen-storage applications, belong to
longstanding challenges of contemporary quantum chemistry. In this respect, the
fixed-node diffusion Monte Carlo (FN-DMC) is a promising alternative to the
commonly used "gold standard" coupled-cluster CCSD(T)/CBS method for its
benchmark accuracy and favourable scaling, in contrast to other correlated wave
function approaches. This work is focused on the analysis of protocols and
possible tradeoffs for FN-DMC estimations of noncovalent interaction energies
and proposes an efficient yet accurate computational protocol using simplified
explicit correlation terms with a favorable O(N^3) scaling. It achieves an
excellent agreement (mean unsigned error ~0.2 kcal/mol) with respect to the
CCSD(T)/CBS data on a number of complexes, including benzene/hydrogen,T-shape
benzene dimer, stacked adenine-thymine and a set of small noncovalent complexes
A24. The high accuracy and reduced computational costs predestinate the
reported protocol for practical interaction energy calculations of large
noncovalent complexes, where the CCSD(T)/CBS is prohibitively expensive.
