Simple corrections for the static dielectric constant of liquid mixtures from model force fields

Cardona, Javier; Jorge, Miguel; Lue, Leo

doi:10.1039/d0cp04034g

Cited by 14 publications

(11 citation statements)

References 75 publications

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“…This has several implications for classical force field development. For instance, the significant enhancement of the liquid dipole moment supports previous assertions by ourselves [11,13,124] and others [8,10,43,123] that classical fixed-charge models should not be expected to yield accurate predictions of the static dielectric constant of water, which depends on the dipole moment surface of the system. Instead, one needs to apply a correction for the fact that the dipole moment of fixed-charge models (normally between 2.2 and 2.4 D) is actually an effective value that is scaled down with respect to the real liquid phase dipole moment (of around 2.8 to 3.0 D) [8,10,11,44].…”

Section: Discussionsupporting

confidence: 76%

Self-consistent electrostatic embedding for liquid phase polarization

Jorge

Gomes

Milne

2021

Journal of Molecular Liquids

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While it is well known that molecules can be strongly polarized when transferred from the gas phase to a polar liquid, quantifying polarization effects explicitly using either experiment or theory has remained elusive. In this paper, we present a new QM/MM method involving a selfconsistent calculation of the liquid state dipole moments, that is able to yield realistic, accurate estimates of the multipole moments of molecules in the liquid state. As a proof-of-concept, we apply our Self-Consistent Electrostatic Embedding (SCEE) method to the widely studied system of pure water. The method gives molecular dipole moments that are significantly enhanced with respect to the isolated gas-phase molecule and that are consistent with the best current experimental estimate of this property. While previous QM/MM calculations on the same system systematically underestimate the liquid dipole moment, those predictions become consistent with our own when several shortcomings are accounted for in an approximate way.Furthermore, sampling liquid configurations using several (but not all) fixed-charge force fields yields results that are consistent with sampling from a classical polarizable model. We then extract several contributions to the polarization energy (i.e. the change in energy when transferring a molecule from the gas to the liquid phase) and show that the distortion correction is cancelled out by the purely electronic contribution to the polarization energy. This insight is very important from the point of view of force-field development, since it allows us to unequivocally quantify the two missing energy terms in classical non-polarizable models. This provides a way to systematically improve predictions of phase-change energies (e.g. enthalpy of vaporization, hydration free energies) from such force-fields by correcting for the missing polarization effects.

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Section: Discussionsupporting

confidence: 76%

Self-consistent electrostatic embedding for liquid phase polarization

Jorge

Gomes

Milne

2021

Journal of Molecular Liquids

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“…Predictions of the dielectric constant were quite good, provided that polarization effects were taken into account—if not, this property was severely underestimated, as shown previously. 46 , 47 For the only molecule for which experimental self-diffusion data was available, namely, tetramethylsilane, the agreement between simulation and experiment was very good. This bodes well for the transferability of the model to other organosilicates containing the same functional groups.…”

Section: Discussionmentioning

confidence: 85%

“…The good agreement observed is further evidence that polarization corrections are important in predicting the dielectric constant, as shown for other families of liquids. 46 , 47 …”

Section: Results and Discussionmentioning

confidence: 99%

“…To mitigate those shortcomings, we apply a simple correction to the dielectric constant obtained from the MD simulations (ε Simul ) It has been shown that application of eq 8 to the results obtained from MD simulations using several nonpolarizable force fields can eliminate systematic errors due to the neglect of explicit polarization and yield predictions that are in good agreement with experimental values for a wide variety of pure liquids 46 as well as mixtures. 47 …”

Section: Methodsmentioning

confidence: 99%

“…Because reliable experimental data for organosilicon molecules is rather scarce, at least compared to more commonly studied organic molecules, a significant effort of data collection, analysis, and curation was undertaken, as described in detail in section . A further motivation for this work is the realization that “standard” nonpolarizable force-fields suffer from systematic shortcomings in predictions of phase-change properties (e.g., enthalpy of vaporization, solvation free energy) and electronic properties (e.g., dielectric constant, dipole moment) due to the neglect of explicit polarization. − Inspired by theoretical developments in approximate treatments of polarization effects, we have begun to parametrize a new class of nonpolarizable models for liquids and solutions, which we call PolCAstanding for Polarization-Consistent Approach. , The force-field developed here for organosilicates is entirely consistent with the new PolCA paradigm, and similarly to our recent work, it is based on a United-Atom description of alkane groups. , …”

Section: Introductionmentioning

confidence: 99%

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New Force-Field for Organosilicon Molecules in the Liquid Phase

et al. 2021

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In this paper, we present a new molecular model that can accurately predict thermodynamic liquid state and phase-change properties for organosilicon molecules including several functional groups (alkylsilane, alkoxysilane, siloxane, and silanol). These molecules are of great importance in geological processes, biological systems, and material science, yet no force field currently exists that is widely applicable to organosilicates. The model is parametrized according to the recent Polarization-Consistent Approach (PolCA), which allows for polarization effects to be incorporated into a nonpolarizable model through post facto correction terms and is therefore consistent with previous parametrizations of the PolCA force field. Alkyl groups are described by the United-Atom approach, bond and angle parameters were taken from previous literature studies, dihedral parameters were fitted to new quantum chemical energy profiles, point charges were calculated from quantum chemical optimizations in a continuum solvent, and Lennard-Jones dispersion/repulsion parameters were fitted to match the density and enthalpy of vaporization of a small number of selected compounds. Extensive validation efforts were carried out, after careful collection and curation of experimental data for organosilicates. Overall, the model performed quite well for the density, enthalpy of vaporization, dielectric constant, and self-diffusion coefficient, but it slightly overestimated the magnitude of self-solvation free energies. The modular and transferable nature of the PolCA force field allows for further extensions to other types of silicon-containing compounds.

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