Applications of a perturbation-aware local correlation method to coupled cluster linear response properties

Abstract

We have investigated the efficacy of two recently proposed variations of the pair-natural-orbital approach to reducing the scaling of coupled cluster property calculations. In particular, we have extended our implementations of the PNO++ and combined PNO++ methods, which make use of field-aware pair-densities to define the virtual-orbital spaces used to describe electron correlation effects, in order to test their accuracy, efficiency, and robustness on larger molecular systems than previously investigated. For fluoroalkane chains up to 1-fluoroheptane we find that the PNO++ and combined PNO++ methods yield smaller truncation errors in response properties than PNO for similarly compact virtual spaces, and, while the PNO method performs better than the PNO++ method for correlation energies, the combined PNO++ method recovers similar accuracy for correlation energies to the PNO method. For more three-dimensional molecular structures such as α- and β − pinenes, the PNO, PNO++, and combined PNO++ methods all yield similar errors for response properties, whereas for (S)-1-phenylethanol, the PNO method performs slightly better than the other two approaches. We also investigate the use of a product density to define the virtual space, as well as two candidates for defining weak-pair contributions.