Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E25: Assigning Structures to Spectra Using Density Functional Theory: Method and Applications IIFocus Live
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Sponsoring Units: DCP Chair: Benjamin Janesko, Texas Christian Univ; Giovanni Scalmani, Gaussian, Inc. |
Tuesday, March 16, 2021 8:00AM - 8:36AM Live |
E25.00001: How Chiroptical Spectroscopy can determine molecular structure Invited Speaker: James Cheeseman Vibrational circular dichroism (VCD) and Raman optical activity (ROA) arise from the differential absorption and scattering, respectively, for left and right circularly polarized light. Although these two chiroptical spectroscopic methods play a fundamental role in the determination of absolute configuration, this presentation will highlight a few recent applications which illustrate how these two methods can be applied to extract additional structural information. Examples include a pair of 22-residue antiparallel double-stranded β-helical species and a series of alanine-rich peptides which form α-helices in water. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E25.00002: Origin Invariant Optical Rotation Tensor in the Length Dipole Gauge without London Atomic Orbitals Marco Caricato We present an approach to perform origin invariant optical rotation calculations in the length dipole gauge without recourse to London atomic orbitals, called origin invariant length gauge [LG(OI)]. The LG(OI) approach works with any approximate wave function or density functional method, but here we focus on the implementation with the coupled cluster (CC) with single and double excitations method because of the lack of production-level alternatives. Preliminary numerical tests show the efficacy of the LG(OI) procedure and indicate that putting the origin in the center of mass of a molecule may not be an optimal choice for conventional CC-LG calculations. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E25.00003: Vibrational Spectroscopy of Intermediates and C-H Activation Products of Sequential Zr+ Reactions with CH4 Justine Kozubal, Tristan Heck, Ricardo B. Metz Vibrational spectra of the entrance channel complexes Zr+(CH4)n(Ar) (n=1-2), Zr+(CH4)n (n=3-4), and the reaction products ZrC3H10+, ZrC4H13+, ZrC4H14+, and ZrC4H15+ in the C-H stretching region (2550-3100 cm-1) are obtained using photofragment spectroscopy. The experimental spectra and simulations based on calculations at the B3LYP/aug-cc-pVTZ level of theory work together to identify the structures of the ions. The n=1-3 entrance channel complexes show peaks around 2800 and 3000 cm-1, while the n=4 complex has two peaks around 2800 cm-1 which indicates different hydrogen coordination. Observation of the low-frequency C-H stretch of an agostic carbene group, as well as the high-frequency H-H stretch, also confirms production of (H2)ZrCH2+(CH4)n-1 (n=1-2) exit channel complexes. The observed C-H activation products correspond to loss of H2 from Zr+(CH4)3 and loss of H, H2, and H2 + H from Zr+(CH4)4. Comparison of experiment and simulations indicate the activation products are Zr(CH3)2+(CH4), Zr(CH3)3+(CH4), Zr(CH3)2+(CH4)2, and HZrCH2+(CH4)3 and/or ZrCH3+(CH4)3. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E25.00004: Microwave driven vapor harvesting with common sorbent materials. Suman Nepal, Aida Shahrokhian, Hunter King Water shortage is a present problem across the world that is anticipated to worsen with a warming climate and growing population. In places where other sources are unreliable, harvesting it directly from the atmosphere is an appealing option. One practical strategy makes use of sorbent materials, whose uptake and release of vapor can be cycled to drive moisture from low to high concentration, thus enabling condensation above the ambient due point. The efficiency of such devices depends on the magnitude and reversibility of the vapor uptake of the sorbent as well as the efficiency of the thermal cycling mechanism. We present a method by which brief exposure to microwave radiation is used to desorb vapor from the sorbent without degrading it, in a custom setup to characterize the performance of sorbent candidates as pertains to their use in concentrating vapor for harvesting. We characterize the performance of ubiquitous and benign material, paper towel, with varying amounts of impregnated hygroscopic salt to demonstrate the method and gain an understanding of the parameters driving performance. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E25.00005: Water molecule dynamics inside the C60 molecular cage. Anna Shugai, Toomas Room, Urmas Nagel, Yasujiro Murata, Salvatore Mamone, Andrea Krachmalnicoff, Malcolm H Levitt, Richard Whitby, Shamim Alom Fullerene molecules encapsulating one H2O molecule have been synthesized using "molecular surgery" [1, 2]. Here we present the low-temperature far- and mid-infrared spectroscopy results of H2O@C60 and C60 solid mixture studies. Para- and ortho-water lines were identified in the rotational and rovibrational spectra of H2O@C60. The vibrational frequencies of confined H2O are red-shifted and the dipole moment is reduced with respect to the gas phase. The center-of-mass quantized translational mode of H2O was observed at about 100 cm-1. The splitting of spectral lines is explained by a model taking into account electrostatic fields present in solid C60 [3]. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E25.00006: Theory of Ultrafast Low-To-High Spin Crossover in Divalent Iron Systems William Baker, Michel A Van Veenendaal A theory is developed for the ultrafast low-to-high spin crossover in divalent iron. As soon as photoexcitation to the metal-to-ligand charge transfer (MLCT) 1A1 state from the 1A1 metal centered (MC) state occurs a sub 100fs decay to the 5T2 iron MLCT through the 3T1 MLCT state and, finally, a transition between MLCT and MC 5T2 states occurs. A fundamental Hamiltonian is constructed but the most important key to a full and fast transition are the damping mechanisms. The significant energy gap between the MLCT states require a rate damping approach centered on phonon movement to fully activate the 5T2 MLCT state but a novel damping approach, Boltzmann damping, is required to overcome the MLCT to MC gap. Whereas destructive interference suppresses spin-orbit-mediated transitions from MLCT to MC states, the Boltzmann damping connects high-energy MLCT states to low-energy MC states of the same symmetry. |
Tuesday, March 16, 2021 9:36AM - 10:12AM Not Participating |
E25.00007: The Virtual Multifrequency Spectrometer: status and perspectives of an ongoing project. Invited Speaker: Vincenzo Barone The impressive advances of computer power, effective and user friendly software and graphical |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E25.00008: An automatic differentiation and diagrammatic notation approach for developing analytical gradients and non-adiabatic couplings of molecular systems Chenchen Song, Todd J Martinez, Jeffrey Neaton Analytical nuclear derivatives and non-adiabatic couplings are important for computational studies of excited state properties of molecular systems . However, its development is increasingly challenging as the complexity of the electronic structure method grows, especially for non-variational methods that preclude the use of the Hellman-Feynman theorem. We show how the combination of automatic differentiation (AD) from computer algebra and diagrammatic notation from quantum circuit models can facilitate the development of analytical nuclear derivatives. In particular, automatically-derived gradients are guaranteed to have the same scaling as the underlying energy calculations, and the computation is roughly three times as costly. The new AD/diagrammatic approach has been applied to our recently proposed supporting subspace multi-reference perturbation theory, providing a balanced treatment of static and dynamic correlation for excited states. We will present an application to green fluorescent protein that show how the selection of QM region affects the excitation energies and shapes of the potential energy surfaces around conical intersections. |
Tuesday, March 16, 2021 10:24AM - 10:36AM On Demand |
E25.00009: Vibrations of Protons and Oxygens in Liquid Water Modeled by Our Melted Ice Hexagonal Close Packed Lattice Bin B. Jie, Cindy Tianhui Jie, Chihtang Sah At the 2013 National Fall Meeting of the Chinese Physical Society, we described our modeling of liquid water by the 1933 Bernal-Fowler Hexagonally Close Packed (HCP) crystalline Ice Model. In the next 6 years we presented our attempted Nonlinear Least Squares Fits (NLSFs) of ~20 models to the experimental data using physics based empirical exponents which gave RMS deviations better than the 10% confidence cited by the experimentalists who obtained the 3 water characterization parameters: the pH or ion product (positive protons and negative prohols) and the two ion's electrical mobilities. We then diagonalized the 36x36 dynamical matrix of the 4H2O in the HCP Primitive Unit Cell (PUC) to give the atomic vibration spectra of the 8 protons and 4 oxygens in the PUC in order to provide a basis for improved NLSFs to the experimental data. This talk gives the normal modes (vibrational frequency and normalized amplitude) in the 4 straight tunnel directions with constant cross-sectional area through the lattice: 1 along the c-axis and 3 120-degree-apart in the ab-plane. Self-traps are added as local modes for 1-step emission-release of a trapped proton by absorbing-capturing a protonic traveling wave-phonon from the kinetic energy source, and vice versa for multistep proton capture. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Not Participating |
E25.00010: Extracting a wave function from experiment: a new approach based on the Coupled Cluster formalism Milaim Kas, Stasis Chuchurka, Andrei Benediktovitch, Tram Do Thi Bich, Christina Brandt, Nina R.G. Rohringer Using experimental data to extract a given wave function is the goal pursued by the field of Quantum Crystalography [1]. Here, scattering data, with a focus on X-ray scattering, are used to constrain a wave function to reproduce experimental results. This approach has been successful to capture electron correlation [2], polarization, crystal field effects [3] and relativistic effects [4] and is currently being developed towards the treatment of larger biological systems [5]. In the present work, we choose a different direction by including spectroscopic data as additional or alternative experimental constraint. The Coupled Cluster and Equation of Motion formalism is used as the underlying theoretical model. Our aim is to develop a general framework from which an experimentally constrained wave function can be calculated. |
Tuesday, March 16, 2021 10:48AM - 11:00AM Not Participating |
E25.00011: Eigenvalues of Uncorrelated, Density-Difference Matrices and the Interpretation of Delta-Self-Consistent-Field Calculations Joseph Ortiz Two theorems on the eigenvalues of differences of idempotent matrices determine the natural occupation numbers and orbitals of electronic detachment, attachment or excitation that pertain to transitions between wavefunctions that each consist of a single Slater determinant. They also are applicable to spin-density matrices associated with Slater determinants. When the ranks of the matrices differ, unit eigenvalues occur. In addition, there are pairs of eigenvalues whose values are related to overlaps between the corresponding orbitals of Amos, Hall and Löwdin by a simple formula . Generalized overlap amplitudes, including Dyson orbitals and their probability factors, may be inferred from these eigenvalues, which provide numerical criteria for: classifying transitions according to the number of holes and particles in final states with respect to initial states, identifying the most important effects of orbital relaxation produced by self-consistent fields and the analysis of Fukui functions. Two similar theorems that apply to sums of idempotent matrices regenerate formulae for the natural orbitals and occupation numbers of an unrestricted Slater determinant that were published first by Amos and Hall. |
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