Born-Oppenheimer molecular dynamics BOMD

Recent advances in first-principles molecular dynamics (MD) calculations, which follow the Newtonian dynamics of classically treated nuclei, have made electronic-structure calculations applicable to the study of large systems where previously only classical simulations were possible. Examples of quantum-mechanical (QM) simulation methods are Born-Oppenheimer molecular dynamics (BOMD), Car-Parrinello molecular dynamics (CPMD), tight-binding molecular dynamics (TBMD), atom-centered density matrix propagation molecular dynamics (ADMPMD), and wavepacket ab idtb molecular dynamics (WPAIMD). 

In order to study the dynamics of small sodium clusters at finite temperatares Born-Oppenheimer molecular dynamics (BOMD) calculations were performed at the above described PBE/DZVP/A2 level of theory. For each cluster, from the dimer to the nonamer, 18 trajectories were recorded in a temperature range from 50 to 900 K with intervals of 50 K. Each trajectory has a length of 220 ps and was recorded with a time step of 2 ps. Similar statistics have already been successfully applied to determine the melting temperatures of sodium clusters with LDA pseudo-potential DFT molecular dynamics (Chacko et al. 2005). 

The first purpose of the present work is thus to evaluate whether the structural distortions which were proposed by Liu et al. [45] are compatible with thermal fluctuations at or near standard room temperature, that is, at 298 and 310 K, according to Maxwell-Boltzmann (MB) statistics [53, 54] on vibrational energy levels. The analysis is supplemented by Born-Oppenheimer Molecular Dynamical (BOMD) simulations [55-57] at the same temperatures of momentum profiles inferred from vertical (e, 2e) ionization cross-sections. A main advantage of this approach is that, by virtue of ergodicity [58], it enables a complete exploration of phase space which is equivalent to an ensemble... 

Often the FPMD schemes are referred to as Born-Oppenheimer (BO) molecular dynamics (BOMD) simulations, since the most often used electronic structure calculation methods employ the separation of time-scales between the nuclear and electronic motions, introduced by Born and Oppenheimer (see discussion at the beginning of section 1.3.1, The Many-Body Problem ). Such BO FPMD simulations have been implemented in several ways [330-334]. 

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