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Accuracy of buffered-force QM/MM simulations of silica

: Peguiron, A.; Colombi Ciacchi, L.; De Vita, A.; Kermode, J.R.; Moras, G.

Volltext urn:nbn:de:0011-n-3366010 (2.7 MByte PDF)
MD5 Fingerprint: a3c6a1a3adb039a90253f144119f50ff
Copyright AIP
Erstellt am: 3.5.2016

The Journal of chemical physics 142 (2015), Nr.6, Art. 064116
ISSN: 0021-9606
European Commission EC
FP7-NMP; 229205; ADGLASS
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IWM ()
silica; chemical bond; electrostatics; quartz; vacancies

We report comparisons between energy-based quantum mechanics/molecular mechanics (QM/MM) and buffered force-based QM/MM simulations in silica. Local quantities-such as density of states, charges, forces, and geometries-calculated with both QM/MM approaches are compared to the results of full QM simulations. We find the length scale over which forces computed using a finite QM region converge to reference values obtained in full quantum-mechanical calculations is similar to 10 angstrom rather than the similar to 5 angstrom previously reported for covalent materials such silicon. Electrostatic embedding of the QM region in the surrounding classical point charges gives only a minor contribution to the force convergence. While the energy-based approach provides accurate results in geometry optimizations of point defects, we find that the removal of large force errors at the QM/MM boundary provided by the buffered force-based scheme is necessary for accurate constrained geometry optimizations where Si-O bonds are elongated and for finite-temperature molecular dynamics simulations of crack propagation. Moreover, the buffered approach allows for more flexibility, since special-purpose QM/MM coupling terms that link QM and MM atoms are not required and the region that is treated at the QM level can be adaptively redefined during the course of a dynamical simulation.