Basis set truncation corrections for improved frozen natural orbital CCSD(T) energies

A number of approaches are proposed and assessed to reduce the frozen natural orbital (FNO) truncation error coupled-cluster singles doubles with perturbative triples [CCSD(T)] energies. The diagrammatic energy decomposition method Irmler Grüneis [J. Chem. Phys. 151, 104107 (2019)] is extended FNO correction particle-particle ladder (PPL) term in case closed- open-shell molecular systems. approach tested for reaction, interaction, atomization energies, it found most robust a wider range thresholds outperforming commonly employed additive MP2 correction. We also show that linear extrapolation (LE) FNO-CCSD(T) energies as function second-order Møller–Plesset (MP2) provides best correlation balanced differences tighter thresholds, but lacks systematic compensation would be required better performance looser thresholds. Further insight gained from spin-component based analysis. Moreover, (pair) specific decompositions utilised introduce size-consistent variants promising PPL LE corrections their analogues (T), which readily applicable context popular local methods.