I want to calculate the density for the $\ce{HCN}$ molecule. This molecule has 14 electrons and thus 7 occupied molecular orbitals. I have a .wfn
file which includes 8 parts, where each of them has 14 rows and 5 columns (due to 5 basis functions). The first part belongs to the basis functions (exponents) and the 7 other parts contain coefficients for each of seven MO's. How can I calculate the electron density using this file? Generally I have used the electron density formula based on the Roothaan expansion introduced in Szabo's textbook, namely:
$$ P_{\mu\nu} =2\sum_{a=1}^{N/2} C_{\mu a}C_{\nu a} $$
where $a$ runs over the number of electrons, though I have seen in several codes that $a$ is considered as the number of occupied MOs. $\mu$ and $\nu$ stand for the number of basis functions (5 here).
Should I use all 7 parts of the coefficients to obtain the electron density of the $\ce{HCN}$ ground state, or is the first part which has the minimum energy sufficient?