Second-order dispersion interactions in π-conjugated polymers

Long considered a failure, second-order symmetry-adapted perturbation theory (SAPT) based on Kohn-Sham orbitals, or SAPT(KS), can been resurrected for semiquantitative purposes using long-range corrected (LRC) density functionals whose asymptotic behavior is adjusted separately for each monomer. As in other contexts, correct asymptotic behavior can be enforced via "optimal tuning" of LRC functionals, based on the ionization energy theorem, but the tuning procedure is tedious, expensive for large systems, and comes with a troubling dependence on system size. Here, we show that essentially identical results are obtained using an automated tuning procedure based on the size of the exchange hole, making tuned "SAPT(wKS)" fast and convenient. In conjunction with SAPT-based methods that sidestep second-order dispersion, this procedure achieves benchmark-quality interaction energies, along with the usual SAPT energy decomposition, without the hassle of system-specific tuning.

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Spin-component-scaled and dispersion-corrected second-order Møller-Plesset perturbation theory: A path toward chemical accuracy

10.33774/chemrxiv-2021-jdv3c ◽

2021 ◽

Author(s):

Chandler Greenwell ◽

Jan Rezac ◽

Gregory Beran

Keyword(s):

Perturbation Theory ◽

Density Functional ◽

Correlation Energy ◽

Computational Cost ◽

Second Order ◽

Spin Component ◽

Dispersion Interactions ◽

Reaction Energies ◽

Moller Plesset ◽

Plesset Perturbation Theory

Second-order Møller-Plesset perturbation theory (MP2) provides a valuable alternative to density functional theory for modeing problems in organic and biological chemistry. However, MP2 suffers from known lim- itations in the description of van der Waals dispersion interactions and reaction thermochemistry. Here, a spin-component-scaled, dispersion-corrected MP2 model (SCS-MP2D) is proposed that addresses these weaknesses. The dispersion correction, which is based on Grimme’s D3 formalism, replaces the uncoupled Hartree-Fock dispersion inherent in MP2 with a more robust coupled Kohn-Sham treatment. The spin- component scaling of the residual MP2 correlation energy then reduces the remaining errors in the model. This two-part correction strategy solves the problem found in earlier spin-component-scaled MP2 models where completely different spin-scaling parameters were needed for describing reaction energies versus in- termolecular interactions. Results on 18 benchmark data sets and two challenging potential energy curves demonstrate that SCS-MP2D considerably improves upon the accuracy of MP2 for intermolecular interac- tions, conformational energies, and reaction energies. Its accuracy and computational cost are competitive with state-of-the-art density functionals such as DSD-BLYP-D3(BJ), revDSD-PBEP86-D3(BJ), ωB97X-V, and ωB97M-V for systems with ∼100 atoms.

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Numerical Analysis of Optical Properties Using Octagonal Shaped Photonic Crystal Fiber

Journal of Optical Communications ◽

10.1515/joc-2019-0013 ◽

2019 ◽

Vol 0 (0) ◽

Author(s):

Ahmed Nabih Zaki Rashed ◽

Mohammed Salah F. Tabbour ◽

P. Vijayakumari

Keyword(s):

Optical Properties ◽

Photonic Crystal ◽

Numerical Analysis ◽

Photonic Crystal Fiber ◽

Propagation Constant ◽

Second Order ◽

Crystal Fiber ◽

Proposed Model ◽

Broadband Spectrum ◽

Order Dispersion

AbstractIn this paper, we propose a design of octagonal photonic crystal fiber with relevant parameters such as effective mode index, propagation constant, second-order dispersion and field distribution of fundamental mode (LP01). The measured parameters can be applied for generating supercontinuum, and also this model is used especially for generating vortex modes and OAM modes in space division multiplexing (SDM) applications. Highly negative dispersion is achieved at −800 ps/nm.km at wavelength of 1.1 μm, and second-order dispersion profile leads to study about the nonlinearity as well as broadband spectrum of the proposed model.

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Evaluating the London Dispersion Coefficients of Protein Force Fields Using the Exchange-Hole Dipole Moment Model

10.26434/chemrxiv.6024410.v1 ◽

2018 ◽

Author(s):

Evan T. Walters ◽

Mohamad Mohebifar ◽

Erin R. Johnson ◽

Christopher Rowley

Keyword(s):

Dipole Moment ◽

Force Fields ◽

Higher Order ◽

Side Chain ◽

Dispersion Interactions ◽

Dispersion Coefficients ◽

Hydration Energies ◽

London Dispersion ◽

Higher Order Dispersion ◽

Order Dispersion

<div>London dispersion is one of the fundamental intermolecular interactions involved in protein folding and dynamics. The popular CHARMM36, Amber ff14sb, and OPLS-</div><div>AA force fields represent these interactions through the C6 /r 6 term of the Lennard-Jones potential. The C6 parameters are assigned empirically, so these parameters are</div><div>not necessarily a realistic representation of the true dispersion interactions. In this work, dispersion coefficients of all three force fields were compared to corresponding</div><div>values from quantum-chemical calculations using the exchange-hole dipole moment (XDM) model. The force field values were found to be roughly 50% larger than the XDM values for protein backbone and side-chain models. The CHARMM36 and Amber OL15 force fields for nucleic acids were also found to exhibit this trend. To explore how these elevated dispersion coefficients affect predicted properties, the hydration energies of the side-chain models were calculated using the staged REMD-TI method of Deng and Roux for the CHARMM36, Amber ff14sb, and OPLS-AA force fields. Despite having large C 6 dispersion coefficients, these force fields predict side-chain hydration energies that are in generally good agreement with the experimental values, including for hydrocarbon residues where the dispersion component is the dominant attractive solute–solvent interaction. This suggests that these force fields predict the correct total strength of dispersion interactions, despite C6 coefficients that are considerably larger than XDM predicts. An analytical expression for the water–methane dispersion energy using XDM dispersion coefficients shows that that higher-order dispersion terms(i.e., C 8 and C 10 ) account for roughly 37.5% of the hydration energy of methane. This suggests that the C 6 dispersion coefficients used in contemporary force fields are</div><div>elevated to account for the neglected higher-order terms. Force fields that include higher-order dispersion interactions could resolve this issue.</div>

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