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
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.