Blackburn, J F; Weaver, P M; Davies, H; Agar, M; Kimmel, A (2010) Project A27: molecular modelling. Final report,. NPL Report. MAT 44

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Abstract

This report describes molecular modelling simulations undertaken as part of the A27 project. Molecular dynamics and Monte Carlo simulations were carried out on a wide variety of material and temperature regimes, from argon at 100 K to the copper/lead binary alloy at 1200K. Also considered are water and CO2 simulations and simulations of the piezoelectric barium titanate. We have not contented ourselves with "snapshots" of simulated atoms in this report. Rather, we believe that molecular simulations must "earn their keep" by providing agreement to experimental findings in accordance with NPL's focus on metrology. Consequently, we have compared all simulation results to experimental data. We have also shown comparison to approximate analytical equations which, in some cases, can rival the accuracy of the molecular codes. In particular, we have focused on reproducing phase diagrams using the molecular models as these are amongst the most striking and characteristic real-world material properties. Phase diagrams considered in this report include temperature-density phase diagrams (ie solid/liquid/gas phase transitions), temperature-molar fraction diagrams (for binary alloys etc) and symmetry phase transitions in piezoelectics (with consequent hysteretic polarisation-electric field plots predicted). We have investigated the ways in which molecular modelling results can help improve predictions made by MTDATA, NPL's flagship commercial materials modelling program. We have shown that the realistic predictions made by the molecular models can be input to mtdata, producing better quality phase diagrams than the ideal gas approximations mtdata would otherwise use. We have written "driver" programs for the modelling codes allowing people who are not experts in molecular simulation to generate phase diagrams through repeated calls to these simulation codes. We have also introduced parallelisation schemes to make use of the NPL Grid. This project acts as a showcase for MDL, a NPL-written molecular dynamics code which is an important piece of IP we could exploit in future. To assess the accuracy of MDL, we have compared it to three other solvers. We have also upgraded MDL, during the course of this project, to support calculation of chemical potentials. These are essential to assess mixing behaviour in gas mixtures (e.g. binary alloys), which are of direct relevance to mtdata. The full set of codes is listed in Table 1.2, which gives links for downloading these programs.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	MAT 44
Subjects:	Advanced Materials Advanced Materials > Materials Modelling
Last Modified:	02 Feb 2018 13:14
URI:	http://eprintspublications.npl.co.uk/id/eprint/4668

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