Nr. 01/2008
Animated Movie of Ice
Melting ice crystals in a computer animation
An animated movie shows an ordered structure dissolving little by little into a disordered mess after a light pulse: Swedish
researchers from the University of Uppsala have used a computer to simulate ice melting after it is heated with a short light
pulse. As they report in the journal Angewandte Chemie, the absorbed energy first causes the OH bonds to oscillate. After a few
picoseconds (10-12 s) the energy is converted into rotational and
translational energy, which causes the crystal to melt, though
crystalline domains remain visible for quite a while.
The common form of ice crystals is known as hexagonal ice. In
this form the oxygen atoms of the water molecules are arranged
in a tetrahedral lattice. Each water molecule is bound to four
neighboring molecules by means of bridging hydrogen bonds,
leading to an average of two bridges per molecule. In water,
there are, on average, only 1.75 bridging hydrogen bonds per
molecule.
What happens in the process of melting? Carl Caleman and
David van der Spoel have now successfully used a computer to
simulate “snapshots” of melting ice crystals. These molecular
dynamics simulations are ideal for gaining a better understanding of processes like melting or freezing because they make it
possible to simultaneously describe both the structure and the
dynamics of a system with atomic resolution and with a time
resolution in the femtosecond (10-15 s) range.
The simulation demonstrated that the energy of the laser pulse
initially causes the OH bonds in the water molecules to vibrate.
Immediately after the pulse, the vibrational energy reaches a
maximum. After about a picosecond, most of the vibrational energy has been transformed into rotational energy. The molecules
begin to spin out of their positions within the crystal, breaking the bridging hydrogen bonds. After about 3 to 6 picoseconds, the rotations diminish in favor
of translational motion. The
-1Angewandte Chemie International Edition ist eine Wiley-VCH-Publikation / is a publication of Wiley-VCH.
Sitz der Wiley-VCH Verlag GmbH & Co. KGaA / Location of company: Weinheim.
Vorsitzender des Aufsichtsrats: John Herbert Jarvis
Handelsregister/Trade Register: Mannheim Abt. B, Nr. 2833 W USt.-Id. Nr. DE 813481633
Steuernummer: 47020 / 21620
Persönlich haftender Gesellschafter: John Wiley & Sons GmbH, Sitz: Weinheim
Amtsgericht Mannheim, Abt. B, Nr. 2296 W, Geschäftsführer: William Pesce
molecules are now able to move freely and the crystal structure
collapses. This process starts out locally, at individual locations
within the crystal. Once the symmetry of the structure is broken,
the likelihood of melting processes occurring in the area immediately surrounding the crystal defect rises significantly. The
melting process thus spreads out from this point little by little.
At other locations the ice can maintain its crystalline structure a
little longer.
(2454 characters)
A movie is available online at http://xray.bmc.uu.se/molbiophys/
images/Movies/melt.mpg
David van der Spoel, Uppsala University (Sweden)
mailto:[email protected]
Picosecond Melting of Ice by an Infrared Laser Pulse: A Simulation Study
Angewandte Chemie International Edition
doi: 10.1002/anie.200703987
Copy free of charge—we would appreciate a transcript of your
article. The original articles that our press releases are based on
and annotated tables of contents of the upcoming issues can be
found ahead of publication in our online pressroom at http://
pressroom.angewandte.org.
-2Angewandte Chemie International Edition ist eine Wiley-VCH-Publikation / is a publication of Wiley-VCH.
Sitz der Wiley-VCH Verlag GmbH & Co. KGaA / Location of company: Weinheim.
Vorsitzender des Aufsichtsrats: John Herbert Jarvis
Handelsregister/Trade Register: Mannheim Abt. B, Nr. 2833 W USt.-Id. Nr. DE 813481633
Steuernummer: 47020 / 21620
Persönlich haftender Gesellschafter: John Wiley & Sons GmbH, Sitz: Weinheim
Amtsgericht Mannheim, Abt. B, Nr. 2296 W, Geschäftsführer: William Pesce