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Surface Hopping Dynamics with Correlated Single-Reference Methods: 9H-Adenine as a Case Study.

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Surface hopping dynamics simulations reveal ultrafast deactivation in 9H-adenine. The algebraic diagrammatic construction (ADC(2)) method accurately captures this process, unlike CC2 and TDDFT, highlighting its suitability for nonadiabatic dynamics.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Theoretical Chemistry

Background:

  • Nonadiabatic processes and excited-state dynamics are crucial in photochemistry and photophysics.
  • Accurate simulation of these processes requires robust computational methods.
  • 9H-adenine is a key biological molecule whose excited-state behavior is of significant interest.

Purpose of the Study:

  • To develop and implement surface hopping dynamics methods using CC2, ADC(2), and TDDFT within the Newton-X program.
  • To investigate the nonadiabatic dynamics of 9H-adenine in the gas phase.
  • To compare the performance of different theoretical methods for simulating excited-state deactivation pathways.

Main Methods:

  • Surface hopping dynamics simulations.
  • Implementation of coupled cluster to approximated second order (CC2), algebraic diagrammatic construction scheme to second order (ADC(2)), and time-dependent density functional theory (TDDFT).
  • Application to 9H-adenine in the gas phase, focusing on excited-state dynamics and conical intersections.

Main Results:

  • ADC(2) dynamics proved stable and accurately predicted the ultrafast deactivation of 9H-adenine.
  • CC2 dynamics exhibited numerical instabilities, failing within 100 fs due to quasi-degenerate excited states.
  • TDDFT with a long-range corrected functional failed to reproduce the ultrafast deactivation.
  • C2-puckered and C6-puckered conical intersections were identified as major internal conversion pathways, with H-elimination playing a minor role.

Conclusions:

  • The ADC(2) method offers a stable and reliable approach for simulating nonadiabatic dynamics, particularly for molecules like 9H-adenine.
  • CC2 and TDDFT methods showed limitations in accurately describing the ultrafast excited-state deactivation of 9H-adenine.
  • ADC(2) provides the most consistent and accurate results for adenine dynamics compared to previously studied methods.