Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H20: Firstprinciples Modeling of Excitedstate Phenomena in Materials VI: Quantum Chemistry and Nonadiabatic DynamicsFocus

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Sponsoring Units: DCOMP DMP Chair: Dorothea Golze, Aalto University Room: BCEC 157A 
Tuesday, March 5, 2019 2:30PM  3:06PM 
H20.00001: Nonorthogonal configuration interaction for molecular excited states: Valence and core excitations and strong correlations Invited Speaker: Martin HeadGordon Most electronic structure methods are designed using a single set of orthogonal orbitals. Using multiple sets of orbitals, that are orthogonal within a given configuration, but nonorthogonal from one configuration to another, is an interesting alternative that is the basis of the nonorthogonal configuration interaction (NOCI) approach to electronic structure. NOCI provides great flexibility to compactly incorporate the different physics of different configurations. A very simple example is a molecule in which an ionic configuration (e.g. Li^{+}F^{}) competes with a covalent configuration (e.g. LiF). Orbital relaxation is very different in the two configurations, and accounts for a large part of what would conventionally be termed dynamic correlation. Far more complicated examples natural arise in mixed valent systems, and systems with lowlying chargetransfer excited states. Core excitations are another natural class of examples. I shall discuss the NOCI method, ways in which it can be made nearly blackbox for interesting classes of valence and core excitations, and how to describe remaining dynamic correlation effects using a generalized second order perturbation theory. A variety of molecular examples will be shown for each of these types of NOCI. I hope to convey the message that the NOCI framework can be very useful for both computing and interpreting electronic structure, with bright prospects for further developments in the future. 
Tuesday, March 5, 2019 3:06PM  3:18PM 
H20.00002: Quantum embedding for excited states in molecular and periodic systems Xuelan Wen, Dhabih Chulhai, Jason Goodpaster Projectionbased quantum embedding methodologies provide a framework for performing DFTinDFT and wavefunctionindensity functional theory (WFinDFT) calculations. The previous application of using absolute localization on the ground states of molecular systems^{1 }and periodic systems^{2 }showed high accuracy and improved computational efficiency. 
Tuesday, March 5, 2019 3:18PM  3:30PM 
H20.00003: Coupled cluster theory for coupled electronphoton systems Uliana Mordovina, Heiko Appel, Angel Rubio, Frederik R. Manby Recent experiments show that properties of materials and energy landscapes of chemical reactions can change drastically when put inside a highQ optical cavity. Understanding these phenomena require novel theoretical approaches, where both parts of the problem, light and matter, are treated on an equal quantum mechanical footing. Extension of existing electronic structure methods to include photons provides one route in this direction. 
Tuesday, March 5, 2019 3:30PM  3:42PM 
H20.00004: A quantum embedding theory in the screened Coulomb interaction: Combining configuration interaction with GW/BSE Marc Dvorak, Patrick Rinke We present a new quantum embedding theory called dynamical configuration interaction (DCI) that combines wave function and Green's function theories. DCI captures static correlation in a correlated subspace with configuration interaction and couples to highenergy, dynamic correlation outside the subspace with manybody perturbation theory based on Green's functions. DCI takes the strengths of both theories to balance static and dynamic correlation in a single, fully abinitio embedding concept. We show that treating highenergy correlation up to the GW and BetheSalpeter equation level is sufficient even for challenging multireference problems. Our theory treats ground and excited states on equal footing, and we compute the dissociation curve of N_{2}, vertical excitation energies of N_{2} and C_{2}, and the ionization spectrum of benzene in excellent agreement with high level quantum chemistry methods and experiment. 
Tuesday, March 5, 2019 3:42PM  3:54PM 
H20.00005: Locality and Computational Reliability of Linear Response Calculations for Molecular Systems Luigi Genovese, Marco D' Alessandro We explore the interplay between locality of the response density operator and numerical convergence of Linear Response quantities. We show that for frequencies below the first ionization potential (IP) of the system, it is possible to express the response density by employing localized states only. Above this threshold energy, such a locality property cannot be achieved. Such considerations may be transposed in terms of the molecule's excited states. We show that not all the system's excitations can be considered on equal footing. There is a discrete sector of excitations  which may extend above IP  that can be parametrized by observable, localized states, which can be computationally expressed with high precision, provided an adequate level of completeness. The remaining excitation modes belong to a continuum spectrum that, on the contrary, is not directly associated to observable properties and can only be effectively represented in a given computational setup. Such considerations are important not only for reproducibility of the results among different computer codes employing diverse formalisms, but also in view of providing a deeper understanding on the impact of models' approximations on the scientific outcomes of the simulation. 
Tuesday, March 5, 2019 3:54PM  4:06PM 
H20.00006: Sticking coefficient for atoms incident upon metals within the exact factorization approach Celso Ricardo Rêgo, Ryan Requist, Luiz Oliveira, Eberhard K U Gross The study of dynamical processes defines one of the busiest frontiers in theoretical CondensedMatter Physics. The TDSE in the BO approximation has often been discussed in this context, but the combination of rapid nuclear motion under imagecharge (IC) potentials with resonances defined by surface shakeups renders the approximation inapplicable. We consider a model based on the AndersonNewns to discuss the collision of a hydrogen atom with a metal and adopt the exactfactorization formalism [1], an approach that has been proven more reliable than the BO approximation, to compute the sticking coefficient as a function of incident energy. In our model, the metal occupies the halfspace z<0, and the adatom impinges upon it along the z axis. The IC potential roughly splits the z>0 in two regions. For z>z_{B}, where z_{B} is a distance of a few Bohr radii, the adatom is neutral and the PES upon which the nucleus moves are flat. For z<z_{B}, the adatom being ionized, the PES are dominated by the IC potential, and the nuclear motion is accompanied by electronhole excitations that dissipate energy and determine the probability of adsorption. We will present the results in the light of this description. 
Tuesday, March 5, 2019 4:06PM  4:18PM 
H20.00007: Coherent State Mapping Ring Polymer Molecular Dynamics for Nonadiabatic Quantum Propagations SUTIRTHA CHOWDHURY, Pengfei Huo Accuartely and efficiently simulating quantum dynamics effects is one of the central challenges in mordern theoretical chemistry. Direct simulations of the exact quantum dynamics remains to be computationally challenging. Here we propose to develop a classical trajectory based method to accurately describe electronic nonadiabatic dynamics as well as capture nuclear quantum effects. This new approach is derived by using coherentstate mapping representation for the electronic degrees of freedom (DOF) and the ringpolymer pathintegral representation for the nuclear DOF. The CSRPMD Hamiltonian does not contain any interbead coupling term in the statedependent potential and correctly describes electronic Rabi oscillations. At the time equivalent to zero, the quantum Boltzmann distribution (QBD) is recovered by reweighting the sampled distribution with an additional phase factor. In a special limit that there is one bead for mapping variables and multiple beads for nuclei, CSRPMD preserves detailed balance and an approximate QBD. Numerical tests of this method with a twostate model system show very good agreement with the exact quantum results. Besides the equlibrium regime, CSRPMD also holds a very promising method to apply in nonequilibrium dynamics. 
Tuesday, March 5, 2019 4:18PM  4:30PM 
H20.00008: QuasiDiabatic scheme for onthefly quantum dynamics propagation Arkajit Mandal, Pengfei Huo We develop a nonadiabatic quantum dynamics scheme to interface diabatic quantum dynamics approaches with adiabatic electronic structure calculation. This scheme uses the crude adiabatic basis as a diabatic basis for a shorttime nuclear dynamics propagation and updates it in each consecutive nuclear step. This scheme extends the scope and applicability of the diabatic quantum dynamics approaches and allows us to propagate onthefly quantum dynamics with them, avoiding any additional nontrivial efforts to perform diabatization or to formulate them back to the adiabatic representation. We combine Partial Linearized Density Matrix approach, a diabatic quantum dynamics method, with Density Functional Tight Binding, an electronic structure approach to demonstrate the applicability of our proposed scheme. 
Tuesday, March 5, 2019 4:30PM  4:42PM 
H20.00009: Electronic NonAdiabatic Dynamics: memorydependence and electronnuclear correlation Ali Abedi Khaledi TimeDependent Density Functional Theory (TDDFT) is one of the most promising theoretical tools in describing the electronic dynamics. In spite of its great success calculating spectra in the linear response regime, it performs poorly in the case of the strongfield dynamics of atoms and molecules. Two main obstacles concerning the application of TDDFT to atoms and molecules in ultrashort intense laser pulses are: 
Tuesday, March 5, 2019 4:42PM  4:54PM 
H20.00010: Optical conductivity and charge fluctuation spectroscopy in the time domain Alexander Kemper, Ankit Kumar Using ultrashort laser pulses it is possible to study the dynamics of manybody systems in the time domain. The response functions are often twoparticle correlation functions, including optical or terahertz transmission spectroscopy (current) and charge fluctuation spectroscopy momentum resolved EELS (charge). We have studied twoparticle response functions using functional derivatives within a nonequilibrium Keldysh Green’s function method. This has several advantages over common approaches, most notably the natural inclusion of vertex corrections. We present the equilibrium and nonequilibrium response of a few model systems including electrons interacting with each other and with a bath of phonons, and discuss the implications for experiments. 
Tuesday, March 5, 2019 4:54PM  5:06PM 
H20.00011: Ab initio study of photoinduced phase transitions Chao Lian, Bryan M Wong Ultrafast realtime lattice dynamics is a powerful tool to study the fundamental properties and behavior of solids. Ultrafast electronic dynamics in solids lies at the core of modern condensed matter and materials physics. To construct a practical ab initio method for studying solids under photoexcitation, we developed a momentumresolved realtime timedependent density functional theory algorithm using a numerical atomic basis, together with the implementation of both length and vector gauges of an electromagnetic field. When applied to the simulation of elementary excitations in both bulk and twodimensional materials, different excitation modes are only distinguishable in momentum space. We also discuss various examples of photoinduced phase transitions such as amorphizations, charge density wave enhancements, and ultrafast solidsolid transitions. 
Tuesday, March 5, 2019 5:06PM  5:18PM 
H20.00012: Modeling Excitation Energies of Quantum Dots based on First Principles Data Ezekiel Oyeniyi, Omololu AkinOjo Wave function ab initio methods are prohibitively expensive for determination of excited states of large systems such as quantum dots. In this work, we present a method for determination of excitaton energies of large systems having more than 10,000 electrons. The method is based on the use of a semiempirical hamiltonian appropriately parameterized to reproduce ab initio "EOMCCSD" excitation energies of small systems. The same set of parameters is then extended to the calculation of excited state properties of large systems. Our results compare well with EOMCCSD, TDDFT, and CIS(D) results whenever they are available. 
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