Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K32: Accurate Methods for Vibrational Analysis (C)Focus

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Sponsoring Units: DCP Chair: Julien Bloino Room: BCEC 204A 
Wednesday, March 6, 2019 8:00AM  8:36AM 
K32.00001: Collocation Methods for Computing Vibrational Spectra Invited Speaker: Tucker Carrington When the potential energy surface (PES) does not have a special form (e.g. a sum of products), it is common to use quadrature to compute a vibrational spectrum. Directproduct quadrature grids are most popular. The size of a directproduct grid scales exponentially with the number of atoms and it is not not possible to store values of the PES for molecules with more than 5 atoms. One option is to use a Smolyak quadrature grid. In this talk, I shall present collocation methods with Smolyaktype grids. Collocation has advantages: 1) point selection is less important; 2) no integrals, no quadratures, no weights; 3) easy to use with complicated kinetic energy operators; 4) it can be used with any (the best possible) coordinates and basis functions; 5) in many cases fewer collocation than quadrature points are required; 6) the length of the vectors one must store is reduced. Collocation can be used with the Multiconfiguration TimeDepend ent Hartree (MCTDH) approach. The collocationbased MCTDH method I shall present can be used with general potential energy surfaces. This is imperative if one wishes to compute very accurate spectra. When the basis is good, the accuracy of collocation solutions to the Schroedinger equation is not sensitive to the choice of the collocation points. The original collocationMCTDH (CMCTDH) method [J. Chem. Phys. 148, 044115 (2018)] uses, as is also true in standard MCTDH, a direct product basis. Because we do not rely on having a sumofproducts potential energy surface, we also have a direct product grid. By using generalized hierarchical basis functions, that span the same space as the single particle functions we introduced in the first CMCTDH paper, and a Smolyak grid, we have developed CMCTDH approach that makes it possible to prune both the basis and the grid. 
Wednesday, March 6, 2019 8:36AM  9:12AM 
K32.00002: On a New Path to Computing the Vibrational Spectra of PAHs Invited Speaker: Ryan Fortenberry Polycyclic aromatic hydrocarbons are big, largely amorphous, and ubiquitous. This makes them both incredibly important (notably for environmental science and astrophysics) and incredibly difficult to precisely describe the infrared spectral features of a single unique PAH specimen type in the laboratory. Quantum chemical computations have recently demonstrated the ability to produce vibrational frequencies for a selection of molecules to as good as within 1.0 cm^{1} of experiment and can do so conclusively for a single molecule since only one chemical system is input into the computations. However, these computations are incredibly costly making them applicable only to small molecules. Recent work in our group has shown that newer quantum chemical theory such as explicitly correlated methods (F12b) can be utilized effectively to produce experimentallycomparable vibrational frequencies at a reduced cost, but this still only extends the sizes of the molecules to be studied potentially up to benzene. However, reparamenterized semiempirical methods designed solely to treat hydrocarbons are showing promise in predicting the spectra of small molecules with a significant savings in time. Successes include cC_{3}H_{2}, C_{3}H_{5}^{+}, and HOCO^{+} among others. These methods are currently being extended to PAHs. 
Wednesday, March 6, 2019 9:12AM  9:48AM 
K32.00003: Ab initio methods targeting strong electron and nuclearcorrelation in spectroscopy Invited Speaker: Markus Reiher The density matrix renormalization group (DMRG) has emerged as an important alternative to multiconfigurational selfconsistentfield calculations in molecular spectroscopy, replacing standard complete active space approaches for large orbital spaces. We implemented a spinadapted matrixproductstate (MPS) and operator formulation of the DMRG, which served as a flexible and efficient basis for the development of an MPS stateinteraction approach for optical spectroscopy and of a shorttime resonance Raman spectroscopy model. We extended our approach to vibrational spectroscopy and I will discuss how the DMRG can be exploited to optimize vibrational wave functions expressed as matrix product states. 
Wednesday, March 6, 2019 9:48AM  10:00AM 
K32.00004: Computational Methods for Excited State TimeResolved Vibrational Spectroscopies Alessio Petrone, Federico Coppola, Fulvio Perrella, Nadia Rega Timeresolved Infrared (IR) and Raman^{1} spectroscopies, have become increasingly important in modern chemical, biological, and materials research. This modern focus is primarily due to their capability to study nonequilibrium structural dynamics of ultrafast chemical phenomena.^{2} 
Wednesday, March 6, 2019 10:00AM  10:12AM 
K32.00005: Gadolinium Cation (Gd^{+}) Reaction with CO_{2}: Potential Energy Surface Mapped from Experiment and Theory Maria Demireva, Peter B Armentrout Understanding the activation of CO_{2} is of interest because of the role of CO_{2} as a greenhouse gas and its potential use as a carbon source in chemical synthesis. In gas phase experiments, the interactions and thermochemistry of CO_{2} with metals can be probed without complicating effects from solvent or substrate molecules. Such studies can provide details about the activation processes at a molecular level. This information can potentially be extended to more complicated systems and be valuable in the design of new and improved catalysts. Here, guided ion beam tandem mass spectrometry is used to investigate the energy dependent reaction of gasphase lanthanide gadolinium cation (Gd^{+}) with CO_{2} to form GdO^{+} and CO. Results show that ground state products are formed in an exothermic and barrierless process, with an electronically excited product ion produced efficiently at high collision energies. Additional experiments on the reverse process as well as Gd^{+}(CO_{2}) and OGd^{+}(CO) intermediates allow for an experimental potential energy surface to be determined. Electronic structure calculations help identify the structures and electronic states of these species and help explain the reactivity observed. Periodic trends in reactivity will be briefly discussed. 
Wednesday, March 6, 2019 10:12AM  10:24AM 
K32.00006: Classical Statistics of Quantum Systems: Quantum StateSpace Distributions and their Dynamics Amro Dodin, Adam P. Willard The statistics of open quantum systems are determined by the interplay of classical uncertainty, describing the lack of knowledge of the initial preparation of the system and bath, and quantum uncertainty, originating from the wavemechanical nature of quantum states. In this presentation, a classical probability distribution on quantum state space will be defined that separately encodes classical and quantum sources of uncertainty. The dynamics of such distributions will then be explored, revealing similar properties to Hamiltonian classical mechanics. In particular, the dynamics of closed systems is shown to be incompressible and time reversible, proving a quantum analog to the classical Liouville's theorem and framing quantum microreversibility equivalently to classical systems. This enables the application of tools from classical mechanics, statistical physics and fluid mechanics to quantum systems with applications in quantum information science and quantum thermodynamics. 
Wednesday, March 6, 2019 10:24AM  10:36AM 
K32.00007: Vibronic Structure and Photoelectron Angular Distribution in the Photoelectron Spectrum of ICN SOUMITRA MANNA, Sabyashachi Mishra In some molecular systems, the complex vibronic structure of photoelectron bands demand extensive theoretical and computational efforts to delineate the interactions between vibrational degrees of freedom and electronic motion, further complicated by coupling of orbital and spin momenta of the electrons. The photoelectron spectroscopy of ICN has been a very challenging problem that has received a lot of attention. However, a conclusive interpretation of the spectrum, in particular, the complex spinvibronic structures of the B^{ 2}Π_{3/2 }and B ^{2}Π_{1/2} states, has remained elusive. In this presentation, we will explain the complex vibronic structure of ICN by analyzing the Dyson orbitals corresponding to the ionized electrons. The simulated spectra have been found to successfully reproduce the position and intensities of the main four photoelectron bands along with the associated vibronic structures. The shape resonances seen in the experimental asymmetry parameters and the trends of ionization crosssection with increasing electron kinetic energies are explained in terms of the partial wave analysis of the departing photoelectron and the contribution of allowed photoelectron angular momentum channels to the ensuing photoelectron wave function. 
Wednesday, March 6, 2019 10:36AM  10:48AM 
K32.00008: Quantum Dynamics of Fluorescence Coupled with Surface Plasmon Polaritons and Intramolecular Vibrations Siwei Wang, LiangYan Hsu, Greg Scholes We study quantum dynamics of molecular fluorescence on a metal surface based on macroscopic quantum electrodynamics and explore the Purcell factor including nonMarkovian effect (beyond Fermi’s golden rule). The method we present is general for molecular fluorescence in a variety of plasmonic nanostructures (not limited to metal surfaces). Furthermore, the proposed method allows us to express memory kernels in terms of the parts of surface plasmon polaritons and molecular vibrations and enables us to calculate the kernels via classical electrodynamics, e.g., finitedifference time domain method. We find that, under different strengths of excitonpolariton couplings, the interplay of surface plasmon polaritons and molecular vibrations can lead to distinct characteristics in dynamics. Our study also provides a direction for exploring the effect of vibrational coherence on plasmonenhanced molecular fluorescence. 
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