  The systems with small binding energies and widely distributed in space
bound-state wave functions are considered. Because the interaction potential is
weak and rather localized compared to the characteristic sizes of wave
functions of these systems, the problem of an accurate determination of binding
energy and wave functions is complicated. An essential part of the study is the
development and application of the discrete-variable representation (DVR)
method. This method is based on the determination of basis functions and the
nodes and weights of a quadrature formula in such way that the values of a
function are zero at all these nodes but one. With this representation the time
required for calculating the Hamiltonian matrix elements is substantially
reduced. The binding energies of several systems consisting of helium and
lithium atoms have been obtained using the DVR method.
