2 lines
8.4 KiB
HTML
2 lines
8.4 KiB
HTML
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<title>Theory of Cluster Dynamics</title>
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<li style="margin-top:1px;border-top:1px solid #B0C4DE; "><a href="../index.html">Home</a></li>
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<p><font size="6" color="white"><b>Theory of Cluster Dynamics</b></font><font
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size="5"><br />
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</font><font size="6"> </font><font size="5">The Toulouse -
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Erlangen Collaboration</font></p>
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</div>
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<div id="content">
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<div style="margin:15px;width:770px;border:1px solid gray;float:left;font-size:10px;">
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<div style="width:220px;float:left;text-align:center;"> <a href="../intro.html">1.
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What are clusters? </a> </div>
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<div style="width:220px;float:left;text-align:center;"> <a href="../dynamics.html">
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2. Why study cluster dynamics?</a> </div>
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<div style="width:220px;float:left;text-align:center;font-weight:900;font-size:12px;">
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<a href="our_dynamics.html"> 3. How we deal with cluster dynamics
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<p>Dynamics </p>
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<div style="text-align: center;">
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<div style="text-align: justify;">
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<h1>How we deal with cluster dynamics<br />
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</h1>
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The understanding of the complicated dynamical scenarios
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such as the ones described previously requires dedicated
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theoretical modelling. Cluster physics and even more so
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cluster dynamics lays at the interface of several fields of
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science, especially chemistry and physics. The theory of
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cluster dynamics has thus borrowed inspiration from these
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various domains to develop its own and original methods. <br />
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<br />
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Not surprisingly, a direct transposition of methods well
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developed in a given field only provides guidelines and a
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starter for further developments. Still, it also allows to
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benchmark new developments on well established test cases.
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Cluster dynamics has thus benefited a lot from experience
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gained in chemistry, especially at the side of moderate
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excitation, and in physics for more violent scenarios,
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especially from solid state and nuclear physics. The
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description of cluster dynamics is made difficult by two
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basic problems: The fact that one would like to deal with
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large (although finite) systems and the fact that electrons
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and ions move at awfully different time scales (typically a
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factor 100). This implies huge simulation times to be able
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to resolve simultaneously electronic and ionic dynamics. One
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thus needs both robust and simple approaches to overcome
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these two difficulties of time scales and system size.<br />
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<br />
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<table style="border: 0px; float: left;">
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<tbody>
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<tr>
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<td> <a href="laser.html"> <img alt="laser" src="laser_slide_small.jpg"
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style="border: 0px solid ; width: 527px; height: 275px; float: left;" />
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</a> </td>
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</tr>
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<tr>
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<td align="center"> <b> Fig.1: Irradiation of Na<sub>9</sub><sup>+</sup>
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by a laser pulse (click on figure to watch movie).
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</b> </td>
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</tr>
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</tbody>
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</table>
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In the case of violent excitation, the most robust and
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simple approaches rely on Density Functional Theory, a
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theory developed since the mid 60's for electronic systems
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and which has met impressive successes, in bulk materials as
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well as in finite molecules. <br />
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<br />
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In density functional theory, the complicated many-body
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electronic problem is simplified as it can be shown that the
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one body electronic density constitutes a key ingredient,
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espcially for computing the energy of the system. The
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extension of this theory to truly time-dependent processes
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is more recent and still in development and cluster dynamics
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offers here a fascinating domain of applications and
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testing.<br />
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<br />
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In order to illustrate the capabilities of such methods we
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present here two examples of cluster response to violent
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external excitation. Figure 1 shows the irradiation of Na<sub>9</sub><sup>+</sup>
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by a laser pulse, while Figure 2 displays a collision of Na<sub>9</sub><sup>+</sup>
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with Ar<sup>8+</sup> considered as an energetic projectile.
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The actual dynamical scenarios can be visualized through the
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two movies below (click on the image to download the
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corresponding movie). Various characteristics of the
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dynamics, especially in terms of time scales, are presented
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in both figures. These cartoons demonstrate strong
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interactions between electrons and ions and a complex
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non-adiabatic dynamics.<br />
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<table>
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<tbody>
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<tr>
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<td> <a href="projectile.html"><img alt="projectile"
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src="proj_slide_small.jpg"
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style="border: 0px solid ; width: 518px; height: 276px;" />
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</a> </td>
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<td align="left"> <b> Fig.2: Collision of Na<sub>9</sub><sup>+</sup>
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with Ar<sup>8+</sup></b><b> (click on figure to
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watch movie)</b> </td>
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</tr>
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</tbody>
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</table>
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