  A review of methods for finding general expressions for matrix elements
(non-diagonal with respect to configurations included) of any one- and
two-particle operator for an arbitrary number of shells in an atomic
configuration is given. These methods are compared in various aspects, and the
advantages or shortcomings of each particular method are discussed. Efficient
method to find the abovementioned quantities in LS coupling is presented, based
on the use of symmetry properties of operators and matrix elements in three
spaces (orbital, spin and quasispin), second quantization in coupled tensorial
form, graphical technique and Wick's theorem. This allows to efficiently
account for correlation effects practically for any atom and ion of periodical
table.
