viii CONTENTS
2.2.5 Valence Bond Parameter ................................................ 88
2.2.6 Electron-to-Atom Ratio ................................................. 91
2.2.7 Summary of Empirical Correlations .............................. 92
2.3 Equilibrium Thermodynamic Calculation of
Diffusion Parameters ............................................................... 93
2.3.1 The Activation Volume .................................................. 94
2.3.2 Activation Entropy and Diffusion Frequency ............... 97
2.3.3 Specific Heat of the Activated Complex ....................... 99
2.3.4 Magnitude of Estimated Values ..................................... 99
2.3.5 Reliability of Estimated Parameters .............................. 104
2.4 Summary .................................................................................. 105
Acknowledgment ............................................................................ 105
Appendix 2A. Taylor Series Expansion of ∆G
*
............................ 105
Appendix 2B. Evaluation of Errors in Estimated Parameters ....... 107
2B.1 ∆S
*
.................................................................................. 108
2B.2 u ...................................................................................... 108
2B.3 ∆C
*
V
................................................................................. 108
2B.4 ∆C
*
P
................................................................................. 109
References ....................................................................................... 109
3 Atomistic Computer Simulation of Diffusion ............................ 113
3.1 Introduction ............................................................................... 113
3.2 Atomic Interaction Models ....................................................... 114
3.2.1 Embedded-Atom Method ............................................... 114
3.2.2 Angular-Dependent Potentials ....................................... 116
3.2.3 More Accurate Methods ................................................. 118
3.3 Molecular Statics ..................................................................... 119
3.3.1 Simulation Block and Boundary Conditions ................. 119
3.3.2 Point-Defect Formation Energy ..................................... 120
3.4 Harmonic Approximation ........................................................ 122
3.4.1 Harmonic Entropy of Point Defects .............................. 122
3.4.2 Effect of Boundary Conditions on
Point-Defect Entropy ..................................................... 123
3.4.3 Embedded Cluster Method ............................................ 125
3.4.4 Local Harmonic Approximation .................................... 127
3.4.5 Quasi-Harmonic Approximation .................................... 128
3.5 Equilibrium Defect Concentrations .......................................... 129
3.5.1 Elemental Solids ............................................................ 129
3.5.2 Non-Stoichiometric Compounds ................................... 130
3.5.3 Effect of Pressure ........................................................... 137
3.6 Transition Rate Calculations .................................................... 138
3.6.1 Transition State Theory .................................................. 138
3.6.2 Finding the Saddle Point ................................................ 141
3.7 Kinetic Monte Carlo Simulations ............................................. 143