What is it about?

In recent works on modelling of alkylated quartz surfaces two different forms of the bending potential Si-O-C5H11 were used, the cosine potential and harmonic cosine potential (this work). Sensitivity of the contact angle to this parameter is low, but the Density Functional Theory (DFT) results suggest that the harmonic cosine potential is a better approximation for general purpose simulations (not only wetting) of chemically modified quartz surfaces.

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Why is it important?

Scientific and industrial challenges posed by the energy transition and climate change include efficient implementation of hydrogen and carbon dioxide geo-storage. Molecular level understanding of underlying storage problems can be achieved using adequate models of chemically modified quartz surfaces. Only few attempts were made to model these surfaces using existing and well tested quartz force fields, which were expanded by variety of chemical species represented by the DREIDING force field. In this work DFT substantiated parameters for quartz surfaces chemically modified with variety of molecules represented by the DREIDING force field are obtained. Range of practical situations and technological applications can be simulated and studied with relatively cheap classical molecular dynamics methods.

Perspectives

The contact angle at the tip level of pentyl groups obtained with potential parameters used in this work (Abramov and Iglauer, 2019) and in (Abramov et al., 2019) is practically insensitive to the form of Si-O-C5H11 bending potential (thus results and conclusions of both papers remain equally valid). However, it is calculated and reported that for alkylated quartz surface structure optimized at the DFT level of theory the Si-O-C5H11 angle is 120.9652 degrees, which in absence of experimental data suggests that the best model for the angle bending in general purpose simulations (not only wettability) would be the harmonic cosine potential, which is used in this work (Abramov and Iglauer, 2019).

Aleksandr Abramov
Heriot-Watt University

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This page is a summary of: Application of the CLAYFF and the DREIDING Force Fields for Modeling of Alkylated Quartz Surfaces, Langmuir, April 2019, American Chemical Society (ACS), DOI: 10.1021/acs.langmuir.9b00527.
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