Ab initio molecular dynamics: Theory and Implementation
Ab initio molecular dynamics: Theory and Implementation
Ab initio molecular dynamics: Theory and Implementation
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in terms of their electronic structure 601 .5.6 Matter at Extreme ConditionsA strong advantage of ab <strong>initio</strong> simulations is their predictive power also at extremeconditions, an area where <strong>molecular</strong> <strong>dynamics</strong> relying on fitted potentialmodels might encounter severe difficulties. Thus, high pressures <strong>and</strong> / or high temperaturessuch as those in the earth’s core, on other planets, or on stars can beeasily achieved in the virtual laboratory. This opens up the possibility to studyphase transformations <strong>and</strong> chemical reactions at such conditions 56 . Furthermore,conditions of geophysical <strong>and</strong> astrophysical interest can nowadays be produced inthe real laboratory, using techniques based on diamond anvil cells, shock waves, orlasers. The limitations of these experimental approaches are, however, not so muchrelated to generating the extreme conditions as one might expect, but rather tomeasuring observables.In the virtual laboratory this information is accessible <strong>and</strong> the melting ofdiamond at high pressure 222 , the phase transformation from the antiferromagneticinsulating δ–O 2 phase to a nonmagnetic metallic <strong>molecular</strong> ζ–O 2 phase 557 ,the phase diagram of carbon at high pressures <strong>and</strong> temperatures 261 as well astransformations of methane 13 , carbon monoxide 54 , <strong>molecular</strong> CO 2 267,558 , waterice 363,364,58,50,51,52 , solid 305,337,65,66,333 <strong>and</strong> hot fluid 5 hydrogen, solid Ar(H 2 ) 253under pressure could be probed. Along similar lines properties of a liquid Fe–S mixtureunder earth’s core conditions 11 , the viscosity of liquid iron 690,592 , the soundvelocity of dense hydrogen at conditions on jupiter 6 , the phase diagram of water<strong>and</strong> ammonia up to 7000 K <strong>and</strong> 300 GPa 118 , the laser heating of silicon 570,572<strong>and</strong> graphite 574 etc. were investigated at extreme state points. A review on ab<strong>initio</strong> simulations relevant to minerals at conditions found in the earth’s mantle isprovided in Ref. 683 .5.7 Clusters, Fullerenes, <strong>and</strong> NanotubesInvestigations of clusters by ab <strong>initio</strong> <strong>molecular</strong> <strong>dynamics</strong> were among the firstapplications of this technique. Here, the feasibility to conduct finite–temperaturesimulations <strong>and</strong> in particular the possibility to search globally for minima turnedout to be instrumental 302,31,303,550,517,519 , see e.g. Refs. 16,321,32 for reviews.Such investigations focus more <strong>and</strong> more on clusters with varying composition518,293,199,348,349,161 . Cluster melting is also accessible on an ab <strong>initio</strong> footing84,531,525,526 <strong>and</strong> <strong>molecular</strong> clusters, complexes or cluster aggregates are activelyinvestigated 612,645,613,70,596,597,133,701,524 .Iii–v semiconductor clusters embedded in sodalite show quantum confinement<strong>and</strong> size effects that can be rationalized by ab <strong>initio</strong> simulations 625,95 . Supportedclusters such as Cu n on an MgO(100) surface are found to diffuse by “rolling” <strong>and</strong>“twisting” motions with very small barriers 438 . The diffusion of protonated heliumclusters in various sodalite cages was generated using ab <strong>initio</strong> <strong>dynamics</strong> 198 . Photo–induced structural changes in Se chains <strong>and</strong> rings were generated by a verticalhomo → lumo excitation <strong>and</strong> monitored by ab <strong>initio</strong> <strong>dynamics</strong> 306 . With thediscovery <strong>and</strong> production of finite carbon assemblies ab <strong>initio</strong> investigations of the123