Balanced complete active space choices with the multiconfigurational spin tensor electron propagator method: The vertical ionization potentials of NH2
✍ Scribed by Alexander J. McKellar; Dodi Heryadi; Danny L. Yeager
- Book ID
- 101253086
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 267 KB
- Volume
- 70
- Category
- Article
- ISSN
- 0020-7608
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✦ Synopsis
With electron propagator methods, vertical ionization potentials IPs and electron affinities can be calculated directly. Our implementation, known as the Ž . multiconfigurational spin tensor electron propagator method MCSTEP , is specifically designed for open-shell and highly correlated initial states. The initial state that is usually Ž . used in MCSTEP is a complete active space CAS MCSCF state. We have previously demonstrated that a small balanced CAS is the optimal choice for the MCSTEP initial state. In this article, we examine two ways of determining this balanced CAS for the MCSTEP initial state. With these choices, we calculate the low-lying vertical MCSTEP IPs Ž . of NH and compare them with experiment for the three lowest IPs. With aug-cc-pVTZ, 2 Ž . aug-cc-pVQZ, and extrapolated complete basis set limits, the MCSTEP IPs for both CAS choices are in very good agreement with experiment. We also calculate the next two vertical IPs where no accurate experimental estimates are as yet available. The ''SCFbalanced'' CAS choice is advantageous to use with MCSTEP because of simplicity, while the ''SDCI-balanced'' CAS is appropriate for use with MCSTEP when the initial MCSCF has undesired properties.