研究目的
To assess the performance of the second-order algebraic diagrammatic construction (ADC(2)) method in the simulation of time-resolved photoelectron spectroscopy (TRPES) spectra of molecular Rydberg states, using N-methylmorpholine (NMM) as a test case.
研究成果
The ADC(2) method provides a realistic description of the potential energy surfaces of the relevant excited and ionized states of NMM, as evidenced by the satisfactory agreement between the simulated and experimentally-observed TRPES spectra. The simulations reproduce the fine oscillatory structure of the signal of the 3s state, attributing it to a coherent vibrational wavepacket evolving along the deformation modes of the six-membered ring. The study demonstrates the usefulness of ADC(2) as a tool to aid the interpretation of the TRPES spectra of large organic molecules, despite its systematic underestimation of electron binding energies.
研究不足
The ADC(2) method underestimates electron binding energies by up to a few tenths of an electronvolt. The study also notes the possibility of artificial leakage of zero-point energy from high-frequency vibrational modes to low-frequency torsional modes in semiclassical simulations of hydrogen-rich molecules.
1：Experimental Design and Method Selection:
The relaxation dynamics of NMM was simulated via the Born-Oppenheimer molecular dynamics (BOMD) method on the potential energy surface of the S1 adiabatic state. The TRPES spectrum was generated based on ionization energies and approximate Dyson orbital norms calculated with the continuum orbital technique.
2：Sample Selection and Data Sources:
The initial conditions for the BOMD simulations were generated by sampling phase space points from the ground-state harmonic-oscillator Wigner distribution of the dominant ground-state conformer of NMM.
3：List of Experimental Equipment and Materials:
The electronic structure of NMM was treated with the use of the M?ller-Plesset perturbation method (MP2) for the singlet ground state in combination with the algebraic-diagrammatic construction scheme of second order (ADC(2)) for the excited states. A custom basis set was applied which was generated from the standard aug-cc-pVDZ basis set.
4：Experimental Procedures and Operational Workflow:
The nuclear dynamics was propagated using the velocity Verlet integrator with a time step of 0.5 fs, for a time period of 1.6 ps. The TRPES spectrum was calculated using the algorithm formulated by Arbelo-González and coworkers.
5：5 fs, for a time period of 6 ps. The TRPES spectrum was calculated using the algorithm formulated by Arbelo-González and coworkers.
Data Analysis Methods:
5. Data Analysis Methods: The raw simulated spectrum obtained was subjected to a Gaussian blur in the time domain with a standard deviation of σ = 25 fs. The intensity maximum in the time interval from 0 to 1500 fs was subjected to the discrete Fourier transform (DFT).
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