Efficient, reliable, ReaxFF+ … molecular dynamics of complex systems
Describing chemical and physical properties of complex systems requires time and length scales which cannot be achieved with pure ab initio methods.
Such processes can be simulated using a reactive force field (Reaxff). The description of inter atomic interactions with analytical functions enables simulations on mesoscopic time and length scales with excellent precision. The challenge is finding the right potential parameters.
Further development and addition of new ReaxFF potential terms is an important part of our work. The ongoing modification and improvement of Reaxff by our developers resulted in the creation of ReaxFF+. The added functionality of ReaxFF+ closes the gap between ab initio methods and classical force fields.
ReaxFF vs. ReaxFF+
Progress is change – thats why our developers are working constantly on the improvement of potential functions and parameter sets. New potential terms based on chemical and physical principals are added and algorithms continuously improved and implemented.
| Potential | ReaxFF | ReaxFF+ | Application (examples) |
|---|---|---|---|
| Van der Waals | dispersive and repulsive forces coupled through parameter (depended on atom type) | dispersive and repulsive forces independently scalable | van der Waals and strong repulsive forces in triple bonds (N2) can be described adequate |
| „Lone-Pair“ energy | shielding for bonds in presence lone-pair | additional term for bond-stabilization in presence of lone-pairs | Description of different bond orders in GaCl and GaCl3 |
| Coulomb Potential | shielding only with atomar parameter | shielding with bond type parameters | improved description of charges in equilibrium |
| Coulomb Potential | shielding only with atomar parameter | additional shielding for string sigma bonds | description of over coordinated ionic complexes possible |
| Coulomb Potential / Charge | general parameter for self repulsion | self repulsion depended on over- and under-coordination of atom | Improved description of ionic fragments and their dissoziation (e.G. H2O -> H+ + OH-) |
Ionic systems in ReaxFF+ - the plus in ReaxFF+
Chemistry without ions – unthinkable!
One feature of ReaxFF is a charge equilibrium scheme to calculate the atomic charges depending on the geometries.
The charge equilibrium scheme implemented in ReaxFF is independent from the bond order, which can result in unphysical bonds with simultaneous ionic and covalent character.
This leads to problems when describing basic and acid solutions or the dissociation of ionic and neutral molecules.
The key enhancement of ReaxFF is the implementation of a charge equilibrium scheme that correlates to the bond order. A correct description of pure ionic and covalent bonds is now possible.
Following figure shows the charge distribution in covalent and ionic bonds. This behavior is achieved by using a shielded Coulomb potential which depends on the bond order.
ReaxFF+ in application
“In theory there is no difference between theory an practice.”
In various projects we have shown that ReaxFF+ can be applied to a wide range of applications:
- crystal growth (MBE, HVPE, CVD …)
- reaction rate in basic an acid solutions
- diffusion of complex molecules
- phase transition and crystallization
- influence of catalyst on reaction rates
- crack formation composite materials
- cooling of polymer melt
- tribology processes
- combustion processes in a reactor
ReaxFF+ custom made
Our mission – finding solutions for your problems. Our large database offers different parameter sets for a wide range of applications. Should no parameter set be available for your specific problem, we have efficient methods at our disposal to create a custom parameters set that fits your needs.
We gladly assist you in the selection of the parameter set, planing of the simulations and create a customized offer for you.
Interest / Questions ...
For further informations please do not hesitate to contact us under:
Tel.: +49 (0)371 / 5347 - 590
Email: plaenitz(at)matcalc.de
