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A pair natural orbital based implementation of CCSD excitation energies within the framework of linear response theory. | LitMetric

AI Article Synopsis

  • The text discusses a new method for calculating excitation energies in quantum chemistry using a Pair Natural Orbital (PNO) approach within the Coupled Cluster Singles and Doubles (CCSD) framework.
  • It involves creating excited state PNOs in a specialized virtual basis to optimize computational efficiency, ensuring smooth results, especially for charge transfer states.
  • The method has been tested on a diverse set of organic molecules, showing promising accuracy with mean absolute errors below 0.01 eV and demonstrating manageable cost-scaling as system size increases.

Article Abstract

We present a pair natural orbital (PNO)-based implementation of coupled cluster singles and doubles (CCSD) excitation energies that builds upon the previously proposed state-specific PNO approach to the excited state eigenvalue problem. We construct the excited state PNOs for each state separately in a truncated orbital specific virtual basis and use a local density-fitting approximation to achieve an at most quadratic scaling of the computational costs for the PNO construction. The earlier reported excited state PNO construction is generalized such that a smooth convergence of the results for charge transfer states is ensured for general coupled cluster methods. We investigate the accuracy of our implementation by applying it to a large and diverse test set comprising 153 singlet excitations in organic molecules. Already moderate PNO thresholds yield mean absolute errors below 0.01 eV. The performance of the implementation is investigated through the calculations on alkene chains and reveals an at most cubic cost-scaling for the CCSD iterations with the system size.

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Source
http://dx.doi.org/10.1063/1.5018514DOI Listing

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