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1. Practical phase-space electronic Hamiltonians for ab initio dynamics

   https://doi.org/10.1063/5.0192084  

   Tao, Zhen; Qiu, Tian; Bhati, Mansi; Bian, Xuezhi; Duston, Titouan; Rawlinson, Jonathan; Littlejohn, Robert G; Subotnik, Joseph E (March 2024, The Journal of Chemical Physics)

   Modern electronic structure theory is built around the Born–Oppenheimer approximation and the construction of an electronic Hamiltonian Ĥel(X) that depends on the nuclear position X (and not the nuclear momentum P). In this article, using the well-known theory of electron translation (Γ′) and rotational (Γ″) factors to couple electronic transitions to nuclear motion, we construct a practical phase-space electronic Hamiltonian that depends on both nuclear position and momentum, ĤPS(X,P). While classical Born–Oppenheimer dynamics that run along the eigensurfaces of the operator Ĥel(X) can recover many nuclear properties correctly, we present some evidence that motion along the eigensurfaces of ĤPS(X,P) can better capture both nuclear and electronic properties (including the elusive electronic momentum studied by Nafie). Moreover, only the latter (as opposed to the former) conserves the total linear and angular momentum in general. 

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2. Linear and angular momentum conservation in surface hopping methods

   https://doi.org/10.1063/5.0179599  

   Wu, Yanze; Rawlinson, Jonathan; Littlejohn, Robert G; Subotnik, Joseph E (January 2024, The Journal of Chemical Physics)

   We demonstrate that, for systems with spin–orbit coupling and an odd number of electrons, the standard fewest switches surface hopping algorithm does not conserve the total linear or angular momentum. This lack of conservation arises not so much from the hopping direction (which is easily adjusted) but more generally from propagating adiabatic dynamics along surfaces that are not time reversible. We show that one solution to this problem is to run along eigenvalues of phase-space electronic Hamiltonians H(R, P) (i.e., electronic Hamiltonians that depend on both nuclear position and momentum) with an electronic–nuclear coupling Γ · P [see Eq. (25)], and we delineate the conditions that must be satisfied by the operator Γ. The present results should be extremely useful as far as developing new semiclassical approaches that can treat systems where the nuclear, electronic orbital, and electronic spin degrees of freedom altogether are all coupled together, hopefully including systems displaying the chiral-induced spin selectivity effect. 

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3. Evolution of the Electronic Gap of Directly Synthesized Versus Mechanically Transferred WS ₂ Monolayer to Multilayer Films

   https://doi.org/10.1002/admi.202401008  

   He, Xu; Tian, Jinpeng; Wu, Wenjing; Butler, Satya; Huang, Shengxi; Xie, Saien; Kahn, Antoine (February 2025, Advanced Materials Interfaces)

   Abstract The electronic properties of 2D materials play a critical role in determining their potential for device applications. Despite rapid developments in 2D semiconductors, studies of fundamental electronic parameters, including the electronic gap and ionization energy, are limited, with significant discrepancies in reported values. The study focuses on tungsten disulfide (WS₂) and investigates the electronic structure of films comprising an increasing number of layers deposited with two different methods: direct synthesis via metal–organic chemical vapor deposition (MOCVD) and additive mechanical transfer of exfoliated single layers. The films are characterized via Raman, UV–vis, and photoluminescence spectroscopies, as well as ultraviolet photoelectron and inverse photoemission spectroscopies (UPS/IPES). The electronic gap of WS₂ is found to decrease from 2.43 eV for the monolayer to 1.97 eV for the trilayer, indicating a bulk transition at the trilayer thickness. This reduction in the electronic gap is primarily due to the downward shift of the conduction band minimum relative to the valence band maximum. A comparative analysis with MOCVD‐grown WS₂ reveals a slightly larger electronic gap for MOCVD‐grown samples, attributed to differences in defect densities. The electronic levels evaluated through UPS/IPES highlight the significant influence of preparation methods on the electronic properties of WS₂. 

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4. Roadmap on methods and software for electronic structure based simulations in chemistry and materials

   https://doi.org/10.1088/2516-1075/ad48ec  

   Blum, Volker; Asahi, Ryoji; Autschbach, Jochen; Bannwarth, Christoph; Bihlmayer, Gustav; Blügel, Stefan; Burns, Lori A; Crawford, T Daniel; Dawson, William; de_Jong, Wibe Albert; et al (May 2024, Electronic Structure)

   Abstract Contents 1. Introduction- Methods and software for electronic structure based simulations of chemistry and materials 2. Density Functional Theory: Formalism and Current Directions 3. Density functional methods - implementation, challenges, successes 4. Green’s function based many-body perturbation theory 5. Wave-function theory approaches – explicit approaches to electron correlation 6. Quantum Monte Carlo and stochastic electronic structure methods 7. Heavy element relativity, spin-orbit physics, and magnetism 8. Semiempirical methods 9. Simulating Nuclear Dynamics with Quantum Effects 10. Real-Time Propagation in Electronic Structure Theory 11. Spectroscopy 12. Tools for exploring potential energy surfaces 13. Managing complex computational workflows 14. Current and Future Computer Architectures 15. Electronic structure software engineering 16. Education and Training in Electronic Structure Theory: Navigating an Evolving Landscape 17. Electronic structure theory facing industry and realistic modeling of experiments 18. List of Acronyms 

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5. Nonadiabatic dynamics with classical trajectories: The problem of an initial coherent superposition of electronic states

   https://doi.org/10.1063/5.0186984  

   Villaseco_Arribas, Evaristo; Maitra, Neepa T; Agostini, Federica (February 2024, The Journal of Chemical Physics)

   Advances in coherent light sources and development of pump–probe techniques in recent decades have opened the way to study electronic motion in its natural time scale. When an ultrashort laser pulse interacts with a molecular target, a coherent superposition of electronic states is created and the triggered electron dynamics is coupled to the nuclear motion. A natural and computationally efficient choice to simulate this correlated dynamics is a trajectory-based method where the quantum-mechanical electronic evolution is coupled to a classical-like nuclear dynamics. These methods must approximate the initial correlated electron–nuclear state by associating an initial electronic wavefunction to each classical trajectory in the ensemble. Different possibilities exist that reproduce the initial populations of the exact molecular wavefunction when represented in a basis. We show that different choices yield different dynamics and explore the effect of this choice in Ehrenfest, surface hopping, and exact-factorization-based coupled-trajectory schemes in a one-dimensional two-electronic-state model system that can be solved numerically exactly. This work aims to clarify the problems that standard trajectory-based techniques might have when a coherent superposition of electronic states is created to initialize the dynamics, to discuss what properties and observables are affected by different choices of electronic initial conditions and to point out the importance of quantum-momentum-induced electronic transitions in coupled-trajectory schemes. 

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