Electron affinities with GPU-accelerated density-fitting EOM-CCSD, approximate EOM-CCSD methods and EOM-CCSD with frozen natural orbitals

This work employs multiple strategies to reduce computational cost or increase computational efficiency in calculating electron affinities (EAs) based on the equation-of-motion coupled-cluster singles and doubles (EOMEA-CCSD) method. To reduce storage requirements and computational time, an EOMEA-CCSD program is developed with terms involving 〈vv‖vv〉 treated with density-fitting and GPU-acceleration using single-precision data. EAs of 24 medium-sized organic molecules related to organic photovoltaics materials are calculated with this program using the aug-cc-pVXZ (X = D, T and Q) basis sets. Results indicate that the basis set incomplete error on the EAs is significant with the DZ basis set, while the EAs obtained with the TZ and QZ basis sets agree well with each other in the EOMEA-CCSD calculations. The approximate EOM-CCSD method, namely, the corr-CIS(<i>D</i>_∞) method with a scaling of N⁵ and storage of OV³, achieves EAs with a mean absolute deviation (MAD) of about 0.18 eV using the QZ basis. EOMEA-CCSD with frozen natural orbitals (FNO) is also employed to reduce computational cost. Results show that the error of the FNO on EAs is the smallest with NOs from the wavefunction of the electron-attached state (eaNO) with CIS(<i>D</i>_∞). The MAD of the EAs is 0.03 eV with eaNO compared with results without FNO when ∼30% virtual orbitals are kept with the QZ basis set. The error of the FNO on the EAs with NOs from the mean density matrix of the electron-attached state with CIS(<i>D</i>_∞) and the MP2 density matrix for the reference is larger than that with eaNO. However, its error on the EAs can be estimated reliably from that of CIS(<i>D</i>_∞), especially with the TZ and QZ basis sets.