Direct to
Information for

 

 

 

 

 

Funded by

 

Results

  • IMD has been enlarged by the potential method of Tagney and Scandalo (TS), so that metal-oxides can be simulated taking influences of the polarizability into account.
  • IMD has been enlarged by the Wolf summation. The linear scaling properties allow a dramatical saving of time (Fig. 1).
  • Using this two options, relevant thermodynamic and structural properties of silica have been reproduced, but up to three orders of magnitude faster than in previous works.
  • Both the TS model and the Wolf summation have been implemented in potfit. Force fields for any metal oxide can be generated.
  • A potential for silica has been reparametrized and validated according to Tagney and Scandalo (Abb. 2). Reducing the cut-off radius about 20 percent, effects a bisection in simulation time (Abb. 1).
  • As an application of the TS model beyond silica, we generated and validated a force field for magnesia. To our knowledge, no other pairwise liquid magnesia force field can simulate this important material as efficiently as our new one.
  • For the subproject B.2 a high quality force field for aluminum oxide has been generated, which was used for crack propagation simulations. Furthermore, the behavior of electric dipole moments in crack propagation simulations ist studied - to our knowledge for the first time.
  • Due to the visualization (subproject D.3) of electrostatic dipole moments in molecular dynamics simulations of metal oxides, the influence of mechanical forces on the dipole-field could be investigated further. This study revealed, how exactly propagating cracks in alumina influence electric dipol-moments. Furthermore, circular waves of dipolar disorder originating from the crack could be revealed (Fig. 4).
  • The model of Streitz und Mintmire has been successfully implemented in IMD. Using the Wolf summation also for the charge optimization, a significant reduction in computing time is achieved. This follows also by the use of the conjugate gradient method in contrast to the original model of Streitz and Mintmire.
  • The charge contribution of a combined metal-oxide system is described correctly (Fig. 3).

 

Fig. 1: CPU time as a function of the number of atoms with both Wolf and Ewald summation method, simulated with IMD: Perfectly linear scaling up to 2.5 million atoms due to the Wolf summation. Simulations with smaller cutoff-radius are once more about two times faster.

Fig. 2: Liquid silica at 3000 Kelvin, simulated with IMD: Grey spheres depict silicon-atoms, each oxygen-atom is represented by its normalized dipole moment. The color coding further emphasizes the orientaion which shows, that there is no total polarization on average.

Fig. 3a: Visualization of a system alumina / alumina oxide.

Fig. 3b: Charge contribution of an interface composed of AlO and Al. The charge values perpendicular to the interface are shown. The charges of the Al-atoms decrease in the metal as one would expect to the value of zero.

Fig. 4: Crack in alumina changing its propagation direction. Visualization uncovers disruption in the field of elektric dipole moments: Circular wave of dipole disorder coming from the crack tip.