The Journal of Physical Chemistry A最新文献

Mass spectrometry (MS) is a fundamental tool for chemical identification. The current in-silico prediction tools can handle broad instrument conditions, large molecular libraries or fragment structures only on a very limited level. In this work, we propose a dual-model machine learning strategy that can solve this problem by jointly a classification model for fragment identification and noise filtering, and a regression model for spectral prediction. With the help of attention mechanism, our method outperforms other algorithms in accuracy and efficiency, providing a deeper understanding of the molecular fragmentation behavior in mass spectra. Our method can facilitate the large-scale in-silico spectra calculations and the analysis of unknown molecular structures, which may promote wider applications for MS.

The self-energy operator of the ab initio Dyson quasiparticle equation generates orbital-relaxation and differential-correlation corrections to Koopmans predictions of electron binding energies. Among the most important corrections are terms that may be expressed as ring and ladder diagrams. Inclusions of such terms in all orders of the fluctuation potential constitute renormalizations. The ability of several renormalized self-energies to predict molecular ionization energies has been tested versus reliable computational and experimental standards. These results reveal the superior accuracy and efficiency of several new-generation electron-propagator methods. They also demonstrate the strengths and weaknesses of self-energies that include ring or ladder renormalizations only and of methods that allow interactions between these terms. Whereas a simplified ladder method produces useful results, its simplified ring counterpart is more computationally efficient, but less accurate. New-generation alternatives to both methods are more accurate and efficient. No adjustable parameters are included in the generation of reference orbitals or in the formulation of the self-energy approximations examined in this work.

In this contribution we present the first local density-fitted multicomponent density functional theory implementation and assess its use for the calculation of anharmonic zero-point energies. Four challenging cases of molecular aggregates are reviewed: deprotonated formic acid trimer, diphenyl ether-tert-butyl alcohol conformers, anisole/methanol and anisole/2-naphtol dimers. These are all cases where a mismatch between the low-temperature computationally predicted minimum and the experimentally determined structure was observed. Through the use of nuclear-electronic orbital energies in the thermodynamic correction, the correct energetic ordering is recovered. For the smallest system, we compare our results to vibrational perturbation theory anharmonically corrected zero-point energy, with perfect agreement for the lower-lying conformers. The performance of the newly developed code and the density fitting errors are also analyzed. Overall, the new implementation shows a very good scaling with system size and the density fitting approximations exhibit a negligible impact.

Real-time propagation methods for chemistry and physics are invariably formulated using variational techniques. The time-dependent bivariational principle (TD-BIVP) is known to be the proper framework for coupled-cluster type methods, and is here studied from a differential geometric point of view. It is demonstrated how two distinct classical Hamilton's equations of motion arise from considering the real and imaginary parts of the action integral. This in turn leads to two distinct bivariational principles for real bivariational approximation submanifolds. Conservation laws and Poisson brackets are introduced, completing the analogy with classical mechanics. Furthermore, the time-dependent univariational principles (the time-dependent variational principle, the McLachlan principle, and the Dirac-Frenkel principle) are reconstructed using the TD-BIVP and a bivariational submanifold on product form. An overview of established real-time propagation methods is given in the context of our formulation of the TD-BIVP, namely time-dependent traditional coupled-cluster theory, orbital-adaptive coupled-cluster theory, time-dependent orthogonal optimized coupled-cluster theory, Brueckner coupled-cluster theory, and equation-of-motion coupled cluster theory.

Real-time propagation methods for chemistry and physics are invariably formulated using variational techniques. The time-dependent bivariational principle (TD-BIVP) is known to be the proper framework for coupled-cluster type methods, and is here studied from a differential geometric point of view. It is demonstrated how two distinct classical Hamilton’s equations of motion arise from considering the real and imaginary parts of the action integral. This in turn leads to two distinct bivariational principles for real bivariational approximation submanifolds. Conservation laws and Poisson brackets are introduced, completing the analogy with classical mechanics. Furthermore, the time-dependent univariational principles (the time-dependent variational principle, the McLachlan principle, and the Dirac–Frenkel principle) are reconstructed using the TD-BIVP and a bivariational submanifold on product form. An overview of established real-time propagation methods is given in the context of our formulation of the TD-BIVP, namely time-dependent traditional coupled-cluster theory, orbital-adaptive coupled-cluster theory, time-dependent orthogonal optimized coupled-cluster theory, Brueckner coupled-cluster theory, and equation-of-motion coupled cluster theory.

The bonding and spectroscopic properties of ULi^+/0/- and UBe^+/0/- to complete the series for UX^+/0/- for X = Li to F were investigated by high-level ab initio SO-CASPT2 and CCSD(T) electronic structure calculations. The low-lying spin-orbit states were obtained at the SA-CASPT2/aQ-PP level; bond dissociation energies (BDEs), ionization energies (IEs), adiabatic electronic affinities (AEAs), and vertical detachment energies (VDEs) were calculated at the Feller-Peterson-Dixon (FPD) level. A dense manifold of low-lying states was predicted for ULi^+/0/- and UBe^+/0/-. The calculated BDEs for ULi (37.7 kJ/mol) and UBe (8.0 kJ/mol) show that UBe is weakly bound. For redox processes, the BDEs increased for ULi⁺ (109.3 kJ/mol), ULi^- (47.4 kJ/mol), UBe⁺ (35.6 kJ/mol), and UBe^- (72.3 kJ/mol). The IE(ULi) = 4.650 eV is lower than IE(Li); the IE(UBe) = 5.901 eV is close to the IE(U) and to the IEs of UB, UC, UN, UO, and UF. The AEAs of ULi (0.708 eV) and UBe (0.989 eV) are lower than those for UB, UC, UN, and UO but higher than that for EA(UF). Natural bond orbital (NBO) calculations show that ULi has the 5f³6d¹7s² configuration for U and 2s¹ for Li, with a small partial negative charge slightly delocalized on U. UBe arises from the U(5f³6d¹7s²) and Be(2s²) electron configurations with no charge separation. The same calculations were made for WX (X = Li, Be, C-F) to enable detailed comparisons of the properties for UX with WX (X = Li-F). For WX, BDE(WX) is higher than that for UX for X = Li to N and lower than BDE(UX) for X = O and F, mostly due to the higher IE of W than U as ionic character becomes more important going from Li to F.

Recent advances in numerically exact quantum dynamics methods have brought the dream of accurately modeling the dynamics of chemically complex open systems within reach. Path-integral-based methods, hierarchical equations of motion, and quantum analog simulators all require the spectral density (SD) of the environment to describe its effect on the system. Here, we focus on the decoherence dynamics of electronically excited species in solution in the common case where nonradiative electronic relaxation dominates and is much slower than electronic dephasing. We show that the computed relaxation rate is highly sensitive to the choice of SD representation─such as the Drude-Lorentz or Brownian modes─or strategy used to capture the main SD features, even when early-time dephasing dynamics remains robust. The key reason is that electronic relaxation is dominated by the resonant contribution from the high-frequency tails of the SD, which are orders of magnitude weaker than the main features of the SD and can vary significantly between strategies. This finding highlights an important, yet overlooked, numerical challenge: obtaining an accurate SD requires capturing its structure over several orders of magnitude to ensure correct decoherence dynamics at both early and late times. To address this, we provide a simple transformation that recovers the correct relaxation rates in quantum simulations constrained by algorithmic or physical limitations on the shape of the SD. Our findings enable a comparison of different numerically exact simulation methods and expand the capabilities of analog simulations of open quantum dynamics.

High-accuracy ab initio thermochemical predictions for the ionization energy of NF₃, the barrier height (to inversion) of NF₃⁺, and the dissociative ionization threshold of NF₃ to NF₂⁺ + F are presented and incorporated into Active Thermochemical Tables. The adiabatic ionization energy of the first ionization band of NF₃, calculated at 12.647 ± 0.010 eV, is at odds with previous experimental interpretations by nearly 0.36 eV due to unfavorable Franck-Condon factors associated with this transition. The barrier (to inversion) height is calculated to be about 0.6 eV lower in energy than the prior interpretation, which instigates a discussion of the supposed vibrational structure of the first ionization band of NF₃. Updated assignments of the photoelectron spectrum are proposed, and the loss in vibrational spacing on the high-energy side of the experimental ionization band is discussed. Rudimentary anharmonic Franck-Condon simulations qualitatively reproduce the broad spectral features observed in experiment.

Recent advances in numerically exact quantum dynamics methods have brought the dream of accurately modeling the dynamics of chemically complex open systems within reach. Path-integral-based methods, hierarchical equations of motion, and quantum analog simulators all require the spectral density (SD) of the environment to describe its effect on the system. Here, we focus on the decoherence dynamics of electronically excited species in solution in the common case where nonradiative electronic relaxation dominates and is much slower than electronic dephasing. We show that the computed relaxation rate is highly sensitive to the choice of SD representation─such as the Drude–Lorentz or Brownian modes─or strategy used to capture the main SD features, even when early–time dephasing dynamics remains robust. The key reason is that electronic relaxation is dominated by the resonant contribution from the high-frequency tails of the SD, which are orders of magnitude weaker than the main features of the SD and can vary significantly between strategies. This finding highlights an important, yet overlooked, numerical challenge: obtaining an accurate SD requires capturing its structure over several orders of magnitude to ensure correct decoherence dynamics at both early and late times. To address this, we provide a simple transformation that recovers the correct relaxation rates in quantum simulations constrained by algorithmic or physical limitations on the shape of the SD. Our findings enable a comparison of different numerically exact simulation methods and expand the capabilities of analog simulations of open quantum dynamics.

High-accuracy ab initio thermochemical predictions for the ionization energy of NF₃, the barrier height (to inversion) of NF₃⁺, and the dissociative ionization threshold of NF₃ to NF₂⁺ + F are presented and incorporated into Active Thermochemical Tables. The adiabatic ionization energy of the first ionization band of NF₃, calculated at 12.647 ± 0.010 eV, is at odds with previous experimental interpretations by nearly 0.36 eV due to unfavorable Franck–Condon factors associated with this transition. The barrier (to inversion) height is calculated to be about 0.6 eV lower in energy than the prior interpretation, which instigates a discussion of the supposed vibrational structure of the first ionization band of NF₃. Updated assignments of the photoelectron spectrum are proposed, and the loss in vibrational spacing on the high-energy side of the experimental ionization band is discussed. Rudimentary anharmonic Franck–Condon simulations qualitatively reproduce the broad spectral features observed in experiment.