156. Elevating density functional theory to chemical accuracy for water simulations through a density-corrected

        many-body formalism. S. Dasgupta, E. Lambros, J.P. Perdew, F. Paesani. Nat. Commun. 12, 6359 (2021). [link]

We present density-corrected SCAN (DC-SCAN) calculations for water which, minimizing density-driven errors,

elevate the accuracy of the SCAN functional to that of coupled cluster theory, the “gold standard” for chemical

accuracy. Building upon the accuracy and efficiency of DC-SCAN within a many-body formalism, we introduce

a data-driven many-body potential energy function, the MB-SCAN(DC) PEF, that is able to quantitatively reproduce

coupled cluster reference values for interaction, binding, and individual many-body energies of water clusters.

Importantly, the properties of liquid water calculated from molecular dynamics simulations carried out with the

MB- SCAN(DC) PEF are found to be in excellent agreement with experiment, which thus demonstrates that

MB-SCAN(DC) is effectively the first DFT-based model that correctly describes water from the gas to the

condensed phase. Since the many-body formalism adopted by the present MB-SCAN(DC) PEF for water is

general, we believe it can open the door to the routine development of data-driven many-body PEFs for predictive

simulations of generic (small) molecules in the gas, liquid, and solid phases.

151. Unraveling the effect of defects, domain size, and chemical doping on photophysics and charge transport in

        covalent organic frameworks. R. Ghosh, F. Paesani. Chem. Sci. 12, 8373 (2021). [link]

Understanding the underlying physical mechanisms that govern charge transport in two dimensional (2D)

covalent organic frameworks (COFs) will facilitate the development of novel COF-based devices for

optoelectronic and thermoelectric applications. In this study, we provide a quantitative characterization of the

intricate interplay between electronic defects, domain sizes, pore volumes, chemical dopants, and 3D

anisotropic charge migration in 2D COFs. We compare our simulations with recent experiments on doped

COF films and establish the correlations between polaron coherence, conductivity, and transport signatures.

By obtaining the first quantitative agreement with the measured absorption spectra of iodine doped

(aza)triangulene-based COF, we highlight the fundamental differences between the underlying microstructure,

spectral signatures, and transport physics of polymers and COFs. Our findings provide conclusive evidence

of why doped COFs exhibit lower conductivity compared to doped polythiophenes. Finally, we propose

new research directions to address existing limitations and improve charge transport in COFs.

150. Vapor-liquid equilibrium of water with the MB-pol many-body potential. M.C. Muniz, T.E. Gartner III, M. Riera,

        C. Knight, S. Yue, F. Paesani, A. Panagiotopoulos. J. Chem. Phys. 154, 211103 (2021). [link]

Among the many existing molecular models of water, the MB-pol many-body potential has emerged as a

remarkably accurate model, capable of reproducing thermodynamic, structural, and dynamic properties across

water's solid, liquid, and vapor phases. In this work, we assessed the performance of MB-pol with respect to

an important set of properties related to vapor-liquid coexistence and interfacial behavior. Through direct

coexistence classical molecular dynamics simulations at temperatures 400 K < T < 600 K, we calculated

properties such as equilibrium coexistence densities, vapor-liquid interfacial tension, vapor pressure, and

enthalpy of vaporization. We found that the MB-pol model predictions are in good agreement with experimental

data, even for temperatures approaching the vapor-liquid critical point; this agreement was largely insensitive

to system size or the rigid vs. flexible treatment of the intramolecular degrees of freedom. These results attest

to the chemical accuracy of MB-pol and its high degree of transferability, thus enabling MB-pol's application

across a large swath of water's phase diagram.

149. Assessing the accuracy of the SCAN functional for water through a many-body analysis of the adiabatic

        connection formula. E. Lambros, J. Hu, F. Paesani. J. Chem. Theory Comput. 17, 3739 (2021). [link]

We present a systematic analysis of the accuracy of a series of SCANα functionals for water, with varying

fractions (α) of exact exchange, which are constructed through the adiabatic connection formula. Our results

indicate that that all SCANα functionals exhibit substantial errors in the representation of the water 2-body

energies. Importantly, the inclusion of exact exchange is found to have opposite effects on the ability

of the SCANα functionals to describe the interaction energies of water clusters with 2D and 3D

hydrogen-bonding arrangements. These errors are found to directly affect the ability of the SCANα

functionals to describe the structure of liquid water at ambient conditions, which is investigated using

explicit many-body models (MB-SCANα) derived from the corresponding SCANα data. It is found that all

MB-SCANα models predict a more compact first hydration shell, which results in a denser liquid with a more

ice-like structure. These apparent opposite trends can be explained by the inability of all SCANα functionals

to provide a balanced description of the water 2B and 3B energies at the fundamental level.

© Paesani Research Group. All rights reserved.

146. Near- and long-term quantum algorithmic approaches for vibrational spectroscopy.

        N.P.D. Sawaya, F. Paesani, D.P. Tabor. Phys. Rev. A 104, 062419 (2021). [link]

Determining the vibrational structure of a molecule is central to fundamental applications in several areas.

However, when significant anharmonicity and mode coupling are present, the problem is classically intractable

for a molecule of just a few atoms. Here, we outline a set of quantum algorithmic methods for solving the

molecular vibrational structure problem for both near- and long-term quantum computers. There are previously

unaddressed characteristics of this problem which require approaches distinct from the commonly studied

quantum simulation of electronic structure: many eigenstates are often desired, states of interest are often

far from the ground state (requiring methods for "zooming in" to some energy window), and transition

amplitudes with respect to a non-unitary Hermitian operator must be calculated. We address these hurdles

and consider problem instances of four vibrational Hamiltonians. Finally and most importantly, we give

analytical and numerical results which strongly suggest that vibrational structure problems will achieve

quantum advantage before electronic structure problems.

147. On the relationship between hydrogen-bonding motifs and the 1b1 splitting in the X-ray emission spectrum

        of liquid water. V.W.D. Cruzeiro, A.P. Wildman, X. Li, F. Paesani. J. Phys. Chem. Lett. 12, 3996 (2021). [link]

The split of the 1b1 peak observed in the X-ray emission (XE) spectrum of liquid water has been the

focus of intense research over the last two decades. Although several hypotheses have been proposed

to explain the origin of the 1b1 splitting, a general consensus has not yet been reached. In this study,

we introduce a novel theoretical/computational approach which, combining path-integral molecular

dynamics (PIMD) simulations carried out with the MB-pol potential energy function and time-dependent

density functional theory (TD-DFT) calculations, correctly predicts the split of the 1b1 peak in liquid

water and not in crystalline ice. A systematic analysis in terms of the underlying local structure of

liquid water at ambient conditions indicates that several different hydrogen-bonding motifs contribute

to the overall XE lineshape in the energy range corresponding to emissions from the 1b1 orbitals,

which suggests that it is not possible to unambiguously attribute the split of the 1b1 peak to only

two specific structural arrangements of the underlying hydrogen-bonding network.

148. Highly accurate many-body potentials for simulations of N2O5 in water: Benchmarks, development, and

        validation. V. Cruzeiro, E. Lambros, M. Riera, R. Roy, F. Paesani, A.W. Götz. J. Chem. Theory Comput. 17, 3931

        (2021). [link]

Dinitrogen pentoxide (N2O5) is an important intermediate in the atmospheric chemistry of nitrogen oxides.

Although there has been much research, the processes that govern the physical interactions between N2O5

and water are still not fully understood at a molecular level. To this end we present the development of MB-nrg

many-body potential energy functions for simulations of N2O5 in water. This MB-nrg model is based on electronic

structure calculations at the coupled cluster level of theory and is compatible with the successful MB-pol model

for water. By assessing binding curves, distortion energies of N2O5, and interaction energies in clusters of N2O5 and

water, we evaluate the importance of two-body and three-body short-range potentials. The results demonstrate

that our MB-nrg model has high accuracy with respect to the coupled cluster reference, outperforms current

density functional theory models, and thus enables highly accurate simulations of N2O5 in aqueous environments.

152. Simulation meets experiment: Unraveling the properties of water in metal-organic frameworks through

        vibrational spectroscopy. K.M. Hunter, J.C. Wagner, M. Kalaj, S.M Cohen, W. Xiong, F. Paesani.

        J. Phys. Chem. C 125, 12451 (2021). [link]

In this study, we characterize the structure and dynamics of water confined in ZIF-90. Through the integration of

experimental and computational infrared (IR) spectroscopy, we probe the structure of heavy water (D2O) adsorbed

in the pores, disentangling the fundamental framework–water and water–water interactions. The analysis of the

IR spectra simulated at both classical and quantum levels indicates that the D2O molecules preferentially interact

with the carbonyl groups of the framework and highlights the importance of including nuclear quantum effects and

taking into account Fermi resonances for a correct interpretation of the OD-stretch band in terms of the underlying

hydrogen-bonding motifs. We demonstrate that computational spectroscopy can be used to gain quantitative,

molecular-level insights into framework–water interactions that determine the water adsorption capacity of MOFs as

well as the spatial arrangements of the water molecules inside the MOF pores which, in turn, are key to the design

of MOF-based materials for water harvesting.

153. General many-body framework for data-driven potentials with arbitrary quantum mechanical accuracy:

        Water as a case study. E. Lambros, S. Dasgupta, E. Palos, S. Swee, J. Hu, F. Paesani.

        J. Chem. Theory Comput. 17, 5635 (2021). [link]

We present a general framework for the development of data-driven many-body (MB) potential energy functions

(MB-QM PEFs) that represent the interactions between small molecules at an arbitrary quantum-mechanical (QM)

level of theory. As a demonstration, a family of MB-QM PEFs for water are rigorously derived from various density

functionals (MB-DFT) as well as from Møller-Plesset perturbation theory (MB-MP2). We demonstrate that all MB-QM

PEFs preserve the same accuracy as the corresponding ab initio calculations, with the exception of those derived

from GGA density functionals. The differences between the DFT and MB-DFT results are traced back to density-driven

errors. We show that this shortcoming may be overcome, within the many-body formalism, by using density-corrected

functionals that provide a more consistent representation of each individual many-body contribution. This is

demonstrated through the development of a MB-DFT PEF derived from density-corrected PBE-D3 data, which more

accurately reproduces the ab initio results.

154. Data-driven many-body models enable a quantitative description of chloride hydration from clusters to bulk.

        A. Caruso, F. Paesani. J. Chem. Phys. 155, 064502 (2021). [link]

We present a new data-driven potential energy function (PEF) describing chloride–water interactions

which is developed within the many-body-energy (MB-nrg) theoretical framework. Besides

quantitatively reproducing low-order many-body energy contributions, the new MB-nrg PEF is able to

correctly predict the interaction energies of small chloride–water clusters calculated at the CCSD(T)

level of theory. Importantly, classical and quantum molecular dynamics simulations of a single chloride

ion in water demonstrate that the new MB-nrg PEF predicts X-ray spectra in close agreement with the

experimental results. Comparisons with a popular empirical model and a polarizable PEF emphasize

the importance of an accurate representation of short-range many-body effects while demonstrating

that pairwise additive representations of chloride–water and water–water interactions are inadequate

for correctly representing the hydration structure of chloride in both gas-phase clusters and solution.

Our results indicate that the MB-nrg PEFs provide realistic descriptions of ionic aqueous systems.

155. MB-Fit: Software infrastructure for data-driven many-body potential energy functions. E.F. Bull-Vulpe, M.

        Riera, A.W. Götz, F. Paesani. J. Chem. Phys. 155, 124801 (2021). [link]

Many-body potential energy functions (MB-PEFs), which integrate data-driven representations of many-body

short-range quantum mechanical interactions with physics-based representations of many-body polarization and

long-range interactions, have recently been shown to provide high accuracy in the description of molecular

interactions, from the gas to the condensed phase. Here, we present MB-Fit, a software infrastructure for the

automated development of MB-PEFs for generic molecules within the TTM-nrg (“Thole-type model energy”)

and MB-nrg (“many-body energy”) theoretical frameworks. Besides providing all the necessary computational

tools for generating TTM-nrg and MB-nrg PEFs, MB-Fit provides a seamless interface with the MBX software,

a many-body energy/force calculator for computer simulations. Given the demonstrated accuracy of the MB-PEFs,

we believe that MB-Fit will enable routine, predictive computer simulations of generic (small) molecules in the gas,

liquid, and solid phases, including, but not limited to, the modeling of isomeric equilibria in molecular clusters,

solvation processes, molecular crystals, and phase diagrams.

157. Topology-mediated enhanced polaron coherence in covalent organic frameworks. R. Ghosh, F. Paesani.

        J. Phys. Chem. Lett. 12, 9442 (2021). [link]

We employ the Holstein model for polarons to investigate the relationship among defects, topology,

Coulomb trapping, and polaron delocalization in covalent organic frameworks (COFs). We find that

intra-sheet topological connectivity and π-column density can override disorder-induced deep traps and

significantly enhance polaron migration by several orders of magnitude in good agreement with recent

experimental observations. The combination of percolation networks and micropores makes trigonal

COFs ideally suited for charge transport followed by kagome/tetragonal, and hexago- nal structures.

By comparing the polaron spectral signatures and coherence numbers of large 3D frameworks having

a maximum of 180 coupled chromophores, we show that controlling nanoscale defects and the location

of the counter anion is critical for the design of new COF-based materials yielding higher mobilities.

Our analysis es- tablishes design strategies for enhanced conductivity in COFs which can be readily

generalized to other classes of conductive materials such as metal-organic frameworks and perovskites.

158. Water capture mechanisms at zeolitic imidazolate framework interfaces. J.C. Wagner, K.M. Hunter, F. Paesani,

        W. Xiong. J. Am. Chem. Soc. 143, 21189 (2021). [link]

Water capture mechanisms of zeolitic imidazolate framework ZIF-90 are revealed by differentiating the water

clustering at interior interfaces of ZIF-90 and the center pore filling step, using vibrational sum-frequency

generation spectroscopy (VSFG) at a one-micron spatial resolution. Spectral lineshapes of VSFG and IR

spectra suggest that OD modes of heavy water in both water clustering and center pore filling steps experience

similar environments, which is unexpected as weaker hydrogen bond interactions are involved in initial water

clustering at interior surfaces. VSFG intensity shows similar dependence on the relative humidity as the

adsorption isotherm, suggesting that water clustering and pore filling occur simultaneously. MD simulations

based on MB-pol corroborate the experimental observations, indicating that water clustering and center pore

filling happen nearly simultaneously within each pore, with water filling the other pores sequentially. The

integration of nonlinear optics with computational simulations provides critical mechanistic insights into the

pore filling mechanism that could be applied to the rational design of future MOFs.