Below you can see a selection of animations and movies made by the group.
You can see more of our videos on our iceLCN Youtube page.
We add new videos regularly, so why not subscribe to our channel?
Quantum hydrogen bonds: We compare the effect of the quantum mechanics of the nuclei on hydrogen bonds with strengths ranging from weak, to intermediate, to strong.
George's supercooled water lecture: Here George shows us how to freeze water instantly. (Credit: Jiri Klimes, www.chem.ucl.ac.uk/ice).
George's salt dissolving lecture: Here George shows us how to dissolve salt. (Credit: Jiri Klimes, www.chem.ucl.ac.uk/ice).
Molecule exchange: water at TiO2 surface: In this movie we study a collection of water molecules interacting with a perfect TiO2(110) surface using ab initio molecular dynamics simulations. No water dissociation is observed. When we zoom in on the interface zone we see that water molecules can jump away from the first layer and go into the second layer. More details can be found in Liu et al, Phys. Rev. B.82, 161415(R) (2010).(Credit: Limin Liu, www.chem.ucl.ac.uk/ice).
Surface mediated proton transfer: This movie shows a surface mediated proton transfer between two equivalent dissociated states of a water dimer on the (001) surface of MgO at temperature 200 K. It involves the concerted exchange of a surface bound proton and a covalently bonded proton between water and hydroxyl. More details can be found in Hu et al, Phys. Chem. Chem. Phys.12, 3953 (2010). (Credit: Xiaoliang Hu, www.chem.ucl.ac.uk/ice)
Fully Quantum Molecular Dynamics Simulations of Molecules on a Metal Surface: The movie shows a path integral molecular dynamics simulation for a mixture of water and hydroxyl molecules adsorbed on a Pt surface.
The quantum nuclear effects are so pronounced that the traditional "ball and stick" representation of the nuclei is lost and it is difficult to distinguish which molecule is water and which is hydroxyl. To really understand why this movie is so exciting why not read more in Li et al, Phys. Rev. Lett.104, 066102 (2010)? (Credit: Xinzheng Li, www.chem.ucl.ac.uk/ice)
How does salt dissolve in water? Here is the answer from first principles electronic structure theory and accelerated dynamics. The large (yellow) chlorine ion at the corner of the crystal leaves first, as it leaves in becomes increasingly coordinated (bonded) to water molecules in the aqueous film above. (Credit: Limin Liu, www.chem.ucl.ac.uk/ice)
A molecular dynamics simulation (specifically "ab initio path integral molecular dynamics simulation" of a H5O2+ complex in the gas phase): Each atom is represented by several "beads". The beads of the central hydrogen are distributed midway between the two oxygens indicated that this is a shared proton and a symmetric hydrogen bond. (Credit: Rosie Kay and Erlend Davidson, www.chem.ucl.ac.uk/ice)
Pentagonal ice in chains: As the structure of the humble snowflake attests to ice crystals normally come in hexagons. However, our simulations (along with experiments from Andrew Hodgson and co-workers at the University of Liverpool) show that ice can come in pentagons too. The movie shows an ab initio molecular dynamics simulation of a chain of water pentagons on a Cu surface. To learn more see Carrasco et al, Nature Mater.8, 427 (2009). (Credit: Javier Carrasco, www.chem.ucl.ac.uk/ice)
A molecule's eye view of ice on a metal surface: This movie illustrates how with a combination of experiment and theory the str
ucture of ice on the nanoscale can be understood. (Credit: Javier Carrasco, www.chem.ucl.ac.uk/ice)
Dissociating a water dimer with computer simulations: We illustrate computer simulations in which a water dimer is pulled apart
or "dissociated". The hydrogen bond holding the dimer together can be stretched by setting increasingly larger spacings between the two water molecules in the dimer. Constraints
are used to keep the distance between the water molecules at each spacing. As the molecules are pulled further apart the forces between them become weaker. The forces between th
e molecules can be used to calculate the energy needed to pull the dimer completely apart. The atomic nuclei can be considered as classical point particles, or as quantum mechani
cal particles. If we treat the nuclei quantum mechanically, we find that the energy needed to pull the dimer apart is significantly lower than when the nuclei are treated as clas
sical particles. In the quantum mechanical treatment of the nuclei, a set of replicas (or "beads"), which are coupled together by springs, represent the system - these are the sm
all dots, shown in the video. The larger spheres show what the simulation would look like if the nuclei were treated as classical point particles. (Credit: Brent Walker, www.chem.ucl.ac.uk/ice)
Classical versus quantum nuclei - water dimer:
Here we compare ways of considering the atomic nuclei in a computer simulation of the water dimer.
In the first part, we treat the nuclei as classical particles. The red spheres represent
oxygen (O) atoms and the white spheres represent hydrogen (H) atoms. We know that the nuclei are in fact
quantum mechanical entities, and so in the second part of the movie, we use a quantum mechanincal treatment
of the nuclei. The technique we use is "path integral molecular dynamics" (PIMD),
in which a set of replicas of the system (often called "beads"), which are coupled together by
springs, are simulated. The small points show the individual PIMD beads; the larger transparent
spheres, the positions of the atoms averaged over all the beads (these are termed the "centroids").
The PIMD reatment allows us to accurately include the quantum mechanical
nature of the nuclei in our simulation. This can be important if light nuclei are involved in the
system, and/or the temperature under consideration is low as the effects of the quantum mechanics
of the nuclei are greater in these cases. It is important to treat the nuclei as quantum particles
in the case of the water dimer considered here because hydrogen atoms, which have the lightest of
all nuclei, are intrinsically involved.
(Credit: Brent Walker, www.chem.ucl.ac.uk/ice)
Classical versus quantum nuclei - HF pentamer:
In this video, we compare simulations of the HF pentamer, with the nuclei treated either
as classical particles, or as quantum mechanical particles using path integral molecular
dynamics (PIMD). On the left side, we see the classical version. The white spheres represent
hydrogen (H) atoms and the green spheres represent fluorine (F) atoms. In the classical
simulation, there are well-defined short (covalent) and long (hydrogen) bonds between the H
and F atoms. During the simulation, the short and long H-F bonds do not rearrange. At this
relatively high temperature (290 K), quite large fluctuations in the overall structure away
from the ideal pentagonal structure can be seen. On the right we see the simulation of the
HF pentamer with the nuclei treated quantum-mechanically. The small spheres show the
individual PIMD beads, the larger transparent spheres show the "centroids" (the averages of
the atomic positions over all the beads). In this quantum simulation, any distinction
between short and long H-F bonds is much harder to make out. The values of the bond length
show that the difference between "short" and "long" H-F bonds is much smaller than when the
nuclei are treated classically, and switch quickly during the simulation.
(Credit: Brent Walker, www.chem.ucl.ac.uk/ice)
