The semicanonical energy ignores contributions from off-diagonal LMO Fock matrix elements. This is analogous to the difference between DLPNO-CCSD(T0) and DLPNO-CCSD(T1). In the case of canonical Hartree-Fock orbitals, the semicanonical (Q) energy is equivalent to the exact (Q) energy, due to canonical Hartree-Fock MOs diagonalizing the Fock matrix. In a prescreening procedure very similar to our DLPNO-(T) algorithm, we first compute Γ abcd ijkl and the semicanonical t abcd ijkl amplitudes at the looser cutoffs (in Algorithm 2) for all quadruplets at a loose QNO tolerance T CUT QNO PRE , defaulting to 10 -5 , with the PAO and RI domains being formed at looser tolerances T CUT DO QUADS PRE = 2 • 10 -2 and T CUT MKN QUADS PRE = 10 -1 , respectively. After computing the energy (Q0) using the looser tolerances, the energy contribution (Algorithms 3 and 4) of every quadruplet ijkl is saved, and for all quadruplets with an energy less than T CUT QUADS WEAK , defaulting to 10 -8 , their energy contribution is summed to form ∆E screened quadruplets .