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IBRION= -1 | 0 | 1 | 2 | 3 | 5 | 6 | 7 | 8 | 44

IBRION= -1 for NSW=0 or NSW=1
= 0 else

IBRION determines how the ions are updated and moved. For IBRION=0, a molecular dynamics is performed, whereas all other algorithms are destined for relaxations into a local energy minimum. For difficult relaxation problems it is recommended to use the conjugate gradient algorithm (IBRION=2), which presently possesses the most reliable backup routines. Damped molecular dynamics (IBRION=3) are often useful when starting from very bad initial guesses. Close to the local minimum the RMM-DIIS (IBRION=1) is usually the best choice. IBRION=5 and IBRION=6 are using finite differences to determine the second derivatives (Hessian matrix and phonon frequencies), whereas IBRION=7 and IBRION=8 use density functional perturbation theory to calculate the derivatives.


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