Assessment of <scp>DLPNO‐CCSD</scp>(T)‐<scp>F12</scp> and its use for the formulation of the <scp>low‐cost</scp> and reliable <scp>L‐W1X</scp> composite method
Bun Chan, Amir Karton
Abstract
Abstract In the present study, we have investigated the performance of RIJCOSX DLPNO‐CCSD(T)‐F12 methods for a wide range of systems. Calculations with a high‐accuracy option [“DefGrid3 RIJCOSX DLPNO‐CCSD(T 1 )‐F12”] extrapolated to the complete‐basis‐set limit using the maug‐cc‐pV[D+d,T+d]Z basis sets provides fairly good agreements with the canonical CCSD(T)/CBS reference for a diverse set of thermochemical and kinetic properties [with mean absolute deviations (MADs) of ~1–2 kJ mol −1 except for atomization energies]. On the other hand, the low‐cost “RIJCOSX DLPNO‐CCSD(T)‐F12D” option leads to substantial deviations for certain properties, notably atomization energies (MADs of up to tens of kJ mol −1 ). With the high‐accuracy CBS approach, we have formulated the L‐W1X method, which further includes a low‐cost core–valence plus scalar‐relativistic term. It shows generally good accuracy. For improved accuracies in specific cases, we advise replacing maug‐cc‐pV( n +d)Z with jun‐cc‐pV( n +d)Z for the calculation of electron affinities, and using well‐constructed isodesmic‐type reactions to obtain atomization energies. For medium‐sized systems, DefGrid3 RIJCOSX DLPNO‐CCSD(T 1 )‐F12 calculations are several times faster than the corresponding canonical computation; the use of the local approximations (RIJCOSX and DLPNO) leads to a better scaling than that for the canonical calculation (from ~6–7 down to ~2–4 for our test systems). Thus, the DefGrid3 RIJCOSX DLPNO‐CCSD(T 1 )‐F12 method, and the L‐W1X protocol that based on it, represent a useful means for obtaining accurate thermochemical quantities for larger systems.