Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 142, Issue 6, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.4907786
Keywords
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Funding
- European Commission [229205 ADGLASS]
- EPSRC HEmS Grant [EP/L014742/1]
- Rio Tinto Centre for Advanced Mineral Recovery based at Imperial College, London
- EPSRC [EP/L027682/1]
- DFG Emmy Noether program [CI 144/2]
- DOE Office of Science User Facility [DE-AC02-06CH11357]
- Engineering and Physical Sciences Research Council [EP/L014742/1, EP/L027682/1] Funding Source: researchfish
- EPSRC [EP/L027682/1, EP/L014742/1] Funding Source: UKRI
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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. (C) 2015 AIP Publishing LLC.
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