Although P is able to perform all the required steps from the calculation of the one-and two-electron integrals to the computation of the sCI energy, interfacing P , at any stage, with other programs is relatively simple. For example, canonical or CASSCF molecular orbitals can be imported from GAMESS, 137 while atomic and/or molecular integrals can be read from text les like . anks to this exibility, some of us are currently developing plugins for performing sCI calculations for periodic systems. TABLE II. Zeroth-order energy E (0) , second-order perturbative correction E and its renormalized version ZE (in hartree) as a function of the number of determinants N det for the ground-state of the chromium dimer Cr 2 computed in the cc-pVQZ basis set. e statistical error, corresponding to one standard deviation, is reported in parenthesis. -2087.734 -2087.738 TABLE III. Wall-clock time (in seconds) to perform a single Davidson iteration and a second-order correction E calculation (which also includes the CIPSI selection) with an increasing number of 48core compute nodes N nodes . e statistical error obtained on E , de ning the stopping criterion, is 0.17 × 10 -3 a.u.