Long-range dispersion forces between molecules subject to attosecond pulses from ab initio calculations

The London-van der Waals dispersion forces arising from instantaneously induced
dipoles in molecules are a key ingredient in a wide range of phenomena in
physics, chemistry, and biology. Therefore, the ability to control and
manipulate dispersion forces between atoms and molecules is of great
importance. Because those dispersion interactions depend crucially on the
electronic properties of the molecular systems, a simple route to achieve this
would consist in manipulating their electronic states. The recent development
of ultra-short optical pulses has given researchers unprecedented control over
the electronic degrees of freedom. These pulses, tailored in their frequency
and envelope, allow the generation of a strongly out of equilibrium population
of electronic states. We show how the Hamacker constants characterizing the
London-van der Waals interaction between two molecules subject to an optical
pulse can be calculated using time-dependent density functional theory (TD-DFT)
or standard quantum chemistry methods and present several test cases of
molecules subjected to IR and UV attosecond pulses.