  We have developed a flexible framework for constructing Jastrow factors which
allows for the introduction of terms involving arbitrary numbers of particles.
The use of various three- and four-body Jastrow terms in quantum Monte Carlo
calculations is investigated, including a four-body van der Waals-like term,
and anisotropic terms. We have tested these Jastrow factors on one- and
two-dimensional homogeneous electron gases, the Be, B, and O atoms, and the
BeH, H$_2$O, N$_2$, and H$_2$ molecules. Our optimized Jastrow factors retrieve
more than 90% of the fixed-node diffusion Monte Carlo correlation energy in
variational Monte Carlo for each system studied.
