http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
First-principles calculations of the response of a material to an intense radiation field
First principles simulations have been performed for the response of Si to high intensity laser pulses, using a new set of computational techniques. The local density approximation is used to treat exchange and correlation elects. Hellmann-Feynman forces are used to calculate the classical motion of the atoms. The coupled time- dependent Schroedinger equations for electrons and Newtonian equations for atoms are integrated with a fifth order Runge-Kutta method. When the pump intensity is high (4.0 x 1012 [W(f:vt2]), the conduction band minimum descends to about 1.0 eV below the valence band maximum, showing a transformation to metallic behavior. This change is observed to occur about 200 femtoseconds after the pump pulse is applied. The simulations also show that when the pump intensity is relatively low (4.0 x 1011 Wjcn0j no significant change in band structure occurs. The simulations demonstrate that it is the displacement of the ions from their equilibrium positions that causes the band structure to change. These displacements, in tun, are caused by the promotion of electrons from the bonding states in the valence bands to the antibonding states in the conduction bands.
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Includes bibliographical references: pages 96-98.