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 A19: Van Der Waals Interactions in Molecules, Materials, and Complex Environments IFocus Live

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Sponsoring Units: DCOMP Chair: Robert Distasio, Cornell University 
Monday, March 15, 2021 8:00AM  8:36AM Live 
A19.00001: A lowcost composite variant of the r2SCAN density functional approximation Invited Speaker: Stefan Grimme The recently proposed second revision of the SCAN meta density functional approximation (DFA) [Furness et al., J. Phys. Chem. Lett. 2020, 11, 8208−8215, termed r2SCAN] is used to construct an efficient composite electronicstructure method termed r2SCAN3c, in analogy to the well established PBEh3c and B973c approaches. It combines the unmodified r2SCAN functional with a specifically adapted def2TZVP Gaussian AObasis, the D4 dispersion model and a readjusted gCP correction for inter and intramolecular BSSE. Due to the inherently higher accuracy of r2SCAN over many other (m)GGAs, further empirical adjustments for covalent bond lengths as in B973c are not required. The performance of r2SCAN3c is evaluated comprehensively on several thousand energy evaluations, i.e., the GMTKN55 thermochemical database, extended benchmarks for noncovalent interactions (e.g., S30L, HB300SPXx10), organometallic reaction energies (MOR41), lattice energies of organic molecules (DMC8, X23) and ices (ICE10), as well as for the adsorption of small molecules on apolar coinage metals and polar surfaces. These tests reveal spectacularly accurate and consistent reaction energies and noncovalent interactions in molecular and periodic systems, as well as particularly outstanding conformational energies. For a suprisingly wide range of chemistry, r2SCAN3c competes with hybrid/QZbased methods at a small fraction (factor of about 100) of computational cost, surpassing the accuracy of its already efficient predecessor B973c at only twice the cost. As other (m)GGAs, r2SCAN3c suffers from effects of the SIE but this is notably reduced as indicated by smaller artificial chargetransfer in various complexes. We thus chose this numerically robust method as our new group default in standard DFT applications for medium to large systems or large scale screening projects. 
Monday, March 15, 2021 8:36AM  8:48AM Live 
A19.00002: Abinitio approaches in surface chemistry: a new vdW metaexchangecorrelation functional Kai Trepte, Johannes Voss The development of exchangecorrelation (XC) functionals has a longstanding history. 
Monday, March 15, 2021 8:48AM  9:00AM Live 
A19.00003: Van der Waals Attraction and Pauli Repulsion: Learning New Tricks from an Old Dog Ornella Vaccarelli, Dmitry Fedorov, Martin Stoehr, Alexandre Tkatchenko The complex interplay of longrange van der Waals (vdW) attraction and shortrange (Pauli) repulsion plays a major role for the structure and dynamics of molecular systems. Arising from different physical origins, these forces do not seem to have a simple connection. Here, we build a consistent approach to study these interactions within the coarsegrained quantum Drude oscillator (QDO) model. This is an efficient tool to describe longrange correlation forces, where response properties of all valence electrons are represented just by a Drude particle. Treating these Drude oscillator particles as indistinguishable, we introduce the Pauli repulsion into this model and evaluate the exchange energy based on the multipole expansion of the Coulomb interaction. This allows us to reveal a remarkable compensation between dispersion and exchange forces for closedshell dimers. The hidden symmetry between these two energies explains the recently discovered relationship between the vdW radius and atomic polarizabilities with a surprising connection between electronic and geometric properties of quantummechanical systems. Altogether, our results pave the way to explore the potential usefulness of the QDO model as a complete building block to develop nextgeneration quantum force fields. 
Monday, March 15, 2021 9:00AM  9:12AM Live 
A19.00004: Attracting Opposites: Promiscuous Ionπ Binding in the Nucleobases Brian Ernst, Robert Distasio, Andrew Sullivan, Ka Un Lao

Monday, March 15, 2021 9:12AM  9:24AM Live 
A19.00005: NENCI2020: A Large Benchmark Database of NonEquilibrium NonCovalent Interactions with an Emphasis on Close Contacts Zachary Sparrow, Brian Ernst, Paul Joo, Ka Un Lao, Robert Distasio In this work, we present NENCI2020: a benchmark database of nonequilibrium noncovalent interaction energies for a large and diverse set of intermolecular complexes. Designed with an emphasis on close contacts, NENCI2020 simultaneously samples both intermolecular distances (spanning 0.71.1x the equilibrium separation) and intermolecular angles for ~150 molecular dimers, yielding ~8,000 benchmark intermolecular interaction energies computed at the CCSD(T)/CBS level. Using SAPT, we demonstrate that NENCI2020 contains a diverse array of binding motifs, making this database wellsuited for testing and developing nextgeneration force fields, density functional theory (DFT) approximations, quantum chemical (QC) methods, and machinelearning based approaches. This is followed by a critical assessment of ~75 DFT and QC methods, in which we find that most of these approaches can describe equilibrium and nearequilibrium intermolecular interaction energies to within chemical accuracy (1 kcal/mol). However, we find that nearly all methods suffer from a rapid and systematic increase in error as the intermolecular distance becomes small, thereby suggesting that more work will be needed to describe intermolecular potential energy surfaces with uniform accuracy. 
Monday, March 15, 2021 9:24AM  9:36AM Live 
A19.00006: Reaching high precision of binding energies in molecular solids using quantum chemistry methods Khanh Ngoc Pham, Jiri Klimes Accurate calculation of binding energies of molecular solids is challenging due to the need to reliably model electron correlations in extended systems. Moreover, the energy differences between different phases or polymorphs are often small, leading to high requirements not only on the accuracy but also on the precision of the numerical setup. To date, two main approaches are in use to obtain binding energies: direct evaluation using periodic boundary conditions (PBC) and manybody expansion (MBE). Here we compare their efficiency on calculations of four molecular solids: ethane, ethylene, and two forms of acetylene using the random phase approximation (RPA) and secondorder MøllerPlesset perturbation theory (MP2). We assess how difficult it is to reach highly precise values (converged with numerical parameters) in the MBE and PBC approaches. The RPA and MP2 binding energies are also compared with reference values obtained using the coupled cluster scheme (CCSD(T)). We find that RPA with singles corrections is more accurate than MP2 for all considered systems. 
Monday, March 15, 2021 9:36AM  9:48AM Live 
A19.00007: Reproducibility of potential energy surfaces of organic/metal interfaces on the example of PTCDA on Ag(111) Lukas Hörmann, Andreas Jeindl, Oliver T. Hofmann The correct geometry is arguably key to studying the properties of molecules adsorbed on metallic substrates. The energetics of molecular adsorption depend on the interplay of various mechanisms: Covalent bonds, charge transfer, Pauli repulsion and vanderWaals (vdW) interactions shape the potential energy surface (PES). Describing PESs with density functional theory (DFT) requires carefully selecting the exchange correlation functional and vdW correction. To explore the robustness of the PES with respect to the choice of the method, we benchmark common local, semilocal and nonlocal functionals in combination with various vdW corrections. We investigate these methods using perylenetetracarboxylic dianhydride (PTCDA) on Ag(111). [1] 
Monday, March 15, 2021 9:48AM  10:00AM Live 
A19.00008: Alkane Adsorption on Pt(111): the Dispersion Interaction on Metal Surfaces Christopher Sheldon, Joachim Paier, Joachim Sauer Alkane adsorption on metal surfaces occurs primarily through the vdWtype dispersion interaction. This is unaccounted for by most DFT methods, with the exception of the vdWfunctionals.^{12} Instead, corrective terms must be added or higherlevel methods used. However, this is a challenge for periodic systems, such as metal surfaces, where few highlevel methods can be applied without prohibitive cost. 
Monday, March 15, 2021 10:00AM  10:12AM Live 
A19.00009: Longrange Correlation Energy in the Interaction of Molecules with Surfaces Alina Umerbekova, Michele Pavanello By exploiting the fluctuationdissipation theorem of DFT and a formally exact decomposition of the densitydensity linear response function evaluated at imaginary frequency, subsystem Density Functional Theory makes an excellent platform for developing nonlocal longrange correlation energy functionals [1,2]. We present a computational protocol to extract embedded C6 coefficients for molecules surrounded by complex environments from a realtime subsystem TDDFT simulation [3]. The C6 coefficients fully account for environmental screening effects through the manybody response [4]. We showcase a pilot calculation of the C6 coefficient of Benzene adsorbed on monolayer MoS2 and we show a surface enhancement of the van der Waals interaction between two benzene molecules nearby a MoS2 surface of 11 meV compared to the interaction estimated from C6 coefficients derived from isolated benzene molecules. 
Monday, March 15, 2021 10:12AM  10:24AM Live 
A19.00010: Toward Systematic Quantum Embedding of Electrons and Charged Harmonic Oscillators Matej Ditte, Matteo Barborini, Alexandre Tkatchenko Many phenomena in physics, chemistry, and biology (solvents, membranes, nanoinclusions) can be described by embedding explicit molecules into an implicit environment. The coupling between both subsystems is typically treated via an approximate electrostatic or polarizable model [1]. Here, we aim at a systematic quantum treatment of molecular and environmental degrees of freedom modelled by a system of merged nuclei/electrons and charged quantum harmonic oscillators (QHOs). For this purpose, we construct a general Hamiltonian describing an embedded electronic domain in an environment of QHOs and present a variational ansatz, describing the full correlated ground state, integrated and optimized through quantum Monte Carlo methods [2]. Since charged QHOs, obtained by mapping manybody interactions onto a single quantum particle, are able to successfully reproduce the longrange response of real matter [3] with a reduced number of degrees of freedom, our new approach opens to the possibility of describing large systems at the full quantum level, yet at a low computational cost, uncovering important quantum effects between the electronic domain and the environment. 
Monday, March 15, 2021 10:24AM  10:36AM Live 
A19.00011: Effective screening of van der Waals interactions in continuous environments Michael Walter, Johannes Fiedler, Stefan Buhmann, Shubham Sharma Computational investigations of supramolecular ordering under electrochemical conditions required density functional theory (DFT) studies of intermolecular potentials in aqueous environment [1]. These interactions are partly of van der Waals (vdW) type where corrections to the usual DFT functionals have to be applied. While the aqueous environment can be conveniently included through a continuum solvent model, the vdW corrections lack this information. Starting from the CasimirPolder Integral [2], we derive simple expressions for the correction of the vdW contribution relative to vacuum. Single point Gauss quadrature leads to the intuitive result, where the vacuum van der Waals C_{6} coefficient is screened by the squared environment's permittivity evaluated near to the resonance frequencies of the interacting particles. 
Monday, March 15, 2021 10:36AM  10:48AM Live 
A19.00012: Second Quantization of ManyBody Dispersion Formalism: Towards Efficient Quantum Modeling of MillionAtom Systems in Complex Environments Matteo Gori, Alexandre Tkatchenko, Philip Kurian Dispersive van der Waals and Casimir interactions play a key role in an accurate description of the structure, stability, and dynamical properties in physical, chemical, and biological systems. In particular, the manybody dispersion (MBD) formalism, relying on a system of electrostatically coupled quantum harmonic oscillators, provides a tool to understand and numerically investigate manybody van der Waals interactions in systems up to tens of thousands of atoms [Chemical Society Reviews 48, 4118 (2019)]. However, the analysis of MBD collective normal modes in such large systems is not trivial. Moreover, it is not easy to define the coupling among such plasmonlike modes with the degrees of freedom of the surrounding environment (phonons, photons, polaritons). We present a quantum field theoretical approach based on second quantization formalism to describe MBD modes. Such a theoretical description i) enables improved computational efficiency, ii) allows a straightforward application of quantum information tools to MBD modes analysis, and iii) provides a suitable framework to describe the interaction of MBD modes with the surrounding environment. This paves the way to describe MBD effects in large systems such as realistic biomolecular complexes in an arbitrary environment. 
Monday, March 15, 2021 10:48AM  11:00AM Live 
A19.00013: Nextgeneration nonlocal van der Waals density functional Timo Thonhauser, Kristian Berland, Debajit Chakraborty In 2004, a seminal paper introduced the first practical nonlocal van der Waals density functional called vdWDF. However, since then, the functional form of vdWDF has remained unchanged. Bringing together different insights from almost two decades of development and testing, we present the nextgeneration nonlocal correlation functional called vdWDF3 [J. Chem. Theory Comput. 16, 5893 (2020)], in which we change the functional form while staying true to the original design philosophy. Although many popular functionals show good performance around the binding separation of van der Waals complexes, they often result in significant errors at larger separations. With vdWDF3, we address this problem by taking advantage of a recently uncovered and largely unconstrained degree of freedom within the vdWDF framework that can be constrained through empirical input, making our functional semiempirical. We benchmark vdWDF3 against a large set of wellstudied test cases, finding good performance in general and a significant improvement in accuracy at larger separations. 
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