The analysis of the @E01986@ distribution in a molecular system based on the orthonormal natural atomic orbitals. Natural populations, \(n_{i}\left(\text{A}\right)\) are the occupancies of the natural atomic orbitals. These rigorously satisfy the @PT07089@: \(0 < n_{i}\left(\text{A}\right) < 2\). The population of an atom \(n\left(\text{A}\right)\) is the sum of natural populations \(n\left(\text{A}\right)=\sum _{\begin{array}{c} \text{A} \end{array}}n_{i}\left(\text{A}\right)\). A distinguished feature of the NPA method is that it largely resolves the @BT06999@ dependence problem encountered in the Mulliken population analysis method.