Development of new computational methodology

The development of new computational methods is expanding the range of research questions that can be addressed in simulations. Examples of our contributions include a model for incorporation of the effects of electronic excitation into classical molecular dynamics technique, a coarse-grained representation of molecular systems accounting for internal molecular degrees of freedom, a mesoscopic model for nanofibrous materials, as well as various multiscale computational approaches combining atomistic, mesoscopic and continuum models.

Acoustic activation of surface processes

One of the new projects in our group is computational and theoretical analysis of acoustic activation of surface processes, such as diffusion, desorption and structural rearrangements. Our first results indicate that nonlinear sharpening of surface acoustic waves may result in a strong enhancement of surface diffusion. These results suggest that the acoustic activation can serve as an effective substitution for heat in a broad range of applications, including chemical catalysis, low temperature thin film growth, and mass spectrometry of heat sensitive molecules.

Mesoscopic modelling of carbon nanotube network materials

Using a mesoscopic model capable of reproducing dynamic behaviour of thousands of interacting nanotubes, we investigate the behavior and properties of carbon nanotube network materials (so-called nanotube “forests” and “buckypaper”). The simulations reproduce spontaneous self-assembly of nanotubes into a continuous network of bundles, reveal the critical role of bending buckling in defining stability of the network structures, provided insights into the heat transport properties and impact resistance of nanotube network materials.

Atomistic modeling of carbon materials

In our recent study of carbon fibers, we investigate the connections between the microstructure (arrangement of graphitic, turbostratic and amorphous regions) and mechanical properties of carbon fibers. The simulations reveal an important role of alignment of structural elements along the fiber axis, as well as the ability of a small amount of graphene to minimize porosity/defects and reinforce the fibers. These computational predictions have been verified in experiments (group of Chris Li) and led to the design of stronger carbon fibers.

Laser-materials interactions: Spallation, phase explosion, plume dynamics

The investigation of the fundamental mechanisms of laser-materials interactions has been a long-term research direction in our group. Computational results have led to the establishment of the role the photomechanical and thermal processes play in short pulse laser ablation, revealed the mechanisms of the nanoparticle and cluster formation at the early stage of the ablation process, provided insights into the processes responsible for laser-induced modification of surface morphology and subsurface microstructure.

Molecular ejection in MALDI and MAPLE

Computational studies of the fundamental mechanisms of laser ablation of molecular systems have direct implications for practical applications, including the matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and matrix-assisted pulsed laser evaporation (MAPLE) technique for thin film deposition. For MALDI, the computational predictions help optimize the ionization and ion extraction approaches, while for MAPLE, the improved understanding of the mechanisms of molecular transfer suggests the ways to improve quality of deposited films.

Laser ablation in liquids: Nanoparticle synthesis and surface modification

The ability of short pulse laser ablation in liquids to produce clean colloidal nanoparticles and unusual surface structures is used in a broad range of practical applications, particularly in catalysis and biomedicine. In our research, we develop advanced computational models for simulation of laser ablation in liquids and use them to uncover the key processes that control the parameters (structure, composition, and size distributions) of colloidal nanoparticles generated by laser ablation in liquids, as well as the structure of laser-modified surfaces.

Material response to strong excitation: Ultrafast melting

Although melting is a common and well-studied phenomenon, the nature of melting under conditions of rapid heating is still a subject of active scientific debates. Our investigations have revealed a strong effect of dynamic pressure relaxation on the mechanisms of short-pulse laser melting and established the limiting velocity of the melting front propagation. These results are motivating new ultrafast diffraction experiments and are serving as a basis for interpretation of experimental data.

Material response to strong excitation: Electron-phonon coupling

As a part of the design of a predictive model for simulation of laser interaction with metals mentioned above, we investigated the electron temperature dependences of the thermophysical properties of metals under conditions of strong electron-phonon nonequilibrium. The results of these calculations have been used in many studies far beyond the field of laser-materials interactions.

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