Ab initio molecular dynamics: Theory and Implementation

5.2 Solids, Polymers, and MaterialsThe first application of Car–Parrinello molecular dynamics 108 dealt with silicon,one of the basic materials in semiconductor industry. Classic solid–state applicationof this technique focus on the properties of crystals, such as those of CuClwhere anharmonicity and off–center displacements of the Cu along the (111) directionswere found to be important to describe the crystal structure as a functionof temperature and pressure 64 . Various properties of solid nitromethane 647 ,crystalline nitric acid trihydrate 602 , solid benzene 420 , stage–1 alkali–graphite intercalationcompounds 286,287 , and of the one-dimensional intercalation compound2HgS•SnBr 2 530 were determined based on first principles. The molecular solid HBrundergoes various phase transitions upon compression. The dynamical behavior ofone of these phases, disordered HBr–I, could be clarified using ab initio moleculardynamics 313 . Structure, phase transitions and short–time dynamics of magnesiumsilicate perovskites were analyzed in terms of ab initio trajectories 670 . The A7 tosimple cubic transformation in As was investigated using ab initio molecular dynamicsat constant–pressure 568 . By applying external pressure the hydrogen sublatticewas found to undergo amorphization in Mg(OH) 2 and Ca(OH) 2 a phenomenonthat was interpreted in terms of frustration 511 . Properties of solid cubane C 8 H 8were obtained in constant pressure simulations and compared to experiment 514 .Ab initio simulations of the graphitization of flat and stepped diamond (111) surfacesuncovered that the transition temperature depends sensibly on the type ofthe surface 327 .Sliding of grain boundaries in aluminum as a typical ductile metal was generatedand analyzed in terms of atomistic rearrangements 432 . Microfracture in a sampleof amorphous silicon carbide was induced by uniaxial strain and found to induce Sisegregation at the surface 226 . The early stages of nitride growth on cubic siliconcarbide including wetting were modeled by depositing nitrogen atoms on the Si–terminated SiC(001) surface 225 .Classical proton diffusion in crystalline silicon at high temperatures was an earlyapplication to the dynamics of atoms in solids 93 . Using the ab initio path integraltechnique 395,399,644,404 , see Sect. 4.4 the preferred sites of hydrogen and muoniumimpurities in crystalline silicon 428,429 , or the proton positions in HCl • nH 2 O crystallinehydrates 516 could be located. The radiation–induced formation of H ⋆ 2 defectsin c–Si via vacancies and self–interstitials was simulated by ab initio molecular dynamics178 . The classical diffusion of hydrogen in crystalline GaAs was followed interms of diffusion paths 668 and photoassisted reactivation of H–passivated Si donorsin GaAs was simulated based on first principles 430 . Oxygen diffusion in p–dopedsilicon can be enhanced by adding hydrogen to the material, an effect that couldbe rationalized by simulations 107 . Ab initio dynamics helped in quantifying thebarrier for the diffusion of atomic oxygen in a model silica host 279 . The microscopicmechanism of the proton diffusion in protonic conductors, in particular Sc–dopedSrTiO 3 and Y–doped SrCeO 3 , is studied via ab initio molecular dynamics, whereis it found that covalent OH–bonds are formed during the process 561 . Ionic diffusionin a ternary superionic conductor was obtained by ab initio dynamics 677 .Proton motion and isomerization pathways of a complex photochromic molecular119