Section: New Results

Extended Universal Force Field

Participants : Svetlana Artemova, Leonard Jaillet, Stephane Redon.

In parallel with the implementation of a Universal Force Field module in SAMSON (see Section 6.10.3 ), we have developed an extension of this force field to allow soft transitions for both topologies and atoms' typizations. In classical UFF topologies and atoms' typizations are set in the initialization phase and remain fixed for the entire simulation. In the proposed extension, they can vary continuously to allow the transition from one given topology to another (see Figure 6 ). This extended UFF combined with the interaction modeling tools already present in SAMSON allows to interactively build and modify molecules while being driven by UFF forces to ensure the relevance of the corresponding structures. The validity of this extended version of UFF was also tested on the same type of benchmarks as those used to test UFF.

Figure 6. An oxygen atom (dashed circle) of the carbonate ion $C{O}_3^{2-}$ is displaced using the interactive simulation framework in SAMSON (center). With standard UFF, the topology remains unchanged which leads to unrealistic geometries (left). With extended UFF, the covalent bond is broken forming a Carbon dioxide $C{O}_2$ and an isolated Oxygen (right).