I have been engaged in a long-term project to apply time-dependent
density functional theory (TDDFT) to electronic systems.

Density functional theory is now the computational paradigm for quantum
mechanical calculations of energies and properties of

molecules and
condensed
matter. The time-dependent theory applies particularly to electronic
excitation
and interactions with

the electromagnetic field. With my collaborator
Kazuhiro
Yabana, we have developed a real-time formalism and a computer

code to
apply
the theory to many observables. In recent years
we have given increased attention to processes involving

high-intensity
laser pulses. TDDFT is the only quantum theory of high-field effects
that is computationally practical for large

systems. One example
of a new application for the theory is coherent phonon production
by laser pulses, "Coherent phonon

generation in
time-dependent density functional theory." . The figure below
shows the electron density in the crystal before

the pulse is
applied and during the pulse.

Another example is
the change in dielectric properties of a solid after it has been
excited by a strong laser pulse. The properties

can be measured
by pump-probe laser experiments, but until now only simplified models
were available to interpret the results.

We have found that
the TDDFT can applied to make numerical pump-probe experiments,
and we can extract quantities such as

the dielectric function
of the excited system. The method is described in our paper,
"Time-dependent density functional theory for

strong
electromagnetic fields in crystalline solids." As an example,
the figure below shows the reflectivity as a function of the

intensity of the pump pulse from the laser. The sharp rise at
high intensity is due to the formation of an electron-hole plasma.

Since the plasma is a conductor, it tends to reflect the incident
radiation.