  We put forward a generalized procedure which allows to restore the bulk-like
electron and hole wave functions localized in certain valleys from the wave
functions of quantum confined electron/hole states obtained in atomistic
calculations of nanostructures. As a demonstration, the procedure is applied to
the lead chalcogenide quantum dots to extract the effective intravalley
Hamiltonian of the exchange interaction for the ground exciton state PbS and
PbSe quantum dots. Renormalization of the anisotropic intravalley matrix
elemets of velocity is also calculated. The results demonstrate that the matrix
elements of intravalley exchange in PbS quantum dots are much more anisotropic
than ones in PbSe.
