  MRChem is a code for molecular electronic structure calculations, based on a
multiwavelet adaptive basis representation. We provide a description of our
implementation strategy and several benchmark calculations. Systems comprising
more than a thousand orbitals are investigated at the HF level of theory, with
an emphasis on scaling properties. With our design, terms which formally scale
quadratically with the system size, in effect have a better scaling because of
the implicit screening introduced by the inherent adaptivity of the method: all
operations are performed to the requested precision, which serves the dual
purpose of minimizing the computational cost and controlling the final error
precisely. Comparisons with traditional Gaussian-type orbitals based software,
show that MRChem can be competitive with respect to performance.
