Atomistic stimulation

Our investigation on a hydrated reaction center was focused on the the dynamics of the P P, transition which occurs before primary charge separation. In the past, time resolved stimulated emission studies in the P -> P region have been carried out on different RC[13, 14]. A common feature obtained in all these studies is that low frequency (less than 200 cm ) nuclear modes are coupled to this photoexcitation. Although it has been shown that the environment surrounding the special pair is responsible for the coherent oscillations found in the spectra[13], no indication on the atomistic origin of these vibrations has been found. 

Atomistic simulation has also been carried out to calculate electric properties of PVDF Two force fields, MSXX and MSXXS, were specifically built up to address this issue [49]. Dielectric constants and dielectric loss were thus computed for both the crystalline and amorphous phases of PVDF. In agreement with experimental data, the ensuing computational results showed that the amorphous phase exhibits a higher dielectric constant than the crystalline phase. This behavior arises fi om rapid changes in the torsion angles, leading to rapid modulation of the dipole moment perpendicular to the chain axis. It is stimulated by the presence of sohton-like defects that diffuse along the chain, as it was revealed by MD simulation [49]. 

The key property that makes phase change materials attractive for applications in nonvolatile memories is the fast crystallization which allows for a full crystallization in PCM devices on the time scale of 10-100 ns. The fact that both nucleation rate and crystal growth velocity are very large has stimulated direct simulations of the crystallization process by DFT-MD [13-16]. Simulations with up to 180-atom cell and periodic boundary conditions shed light on the atomistic mechanism of formation of the crystalline nucleus and on the role of four-membered rings as seeding structures for nucleation [13-16]. 

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