Chapter 7
Ultrafast Laser-Induced Processes Described
by Ab Initio Molecular Dynamics
Leticia González, Philipp Marquetand, Martin Richter,
Jesús González-Vázquez, and Ignacio Sola
Abstract This chapter introduces theoretical methods that integrate the equations
of motion of electrons and nuclei in molecules, including all degrees of freedom
and all types of couplings. We are concerned with methods that treat the electronic
motion quantum-mechanically, by expanding the electronic wave function in a relatively small basis of eigenstates of the Hamiltonian, and the nuclear motion classically, as an ensemble of trajectories each unfolding on a single electronic state at a
given time, but allowing to switch between states. In particular, we focus on a quite
novel method called the SHARC (Surface-Hopping in the Adiabatic Representation
including arbitrary Couplings) scheme. The main novelty of SHARC consists in the
evaluation of the transition probability between electronic states, which is performed
by surface-hopping techniques in the adiabatic representation, essentially treating
on the same footing both non-adiabatic beyond Born-Oppenheimer transitions (intersystem crossing, internal conversion) and laser-induced crossings. The choice of
approximations and representation is particularly useful in evaluating the dynamics
when the laser field or non-adiabatic couplings are strong. In the chapter we show
examples of the performance of the scheme in two scenarios. In the first one, the
dynamics of the system is simulated starting in the electronic excited state assuming
an instantaneous excitation. In the second one, the interaction of the system with
an external laser field is explicitly considered. This approach is necessary when deactivation occurs during the laser excitation. Moreover, the explicit consideration
of the external field permits the use of quantum control schemes. We consider here
two limiting cases, the impulsive and the adiabatic time-evolution, represented by
two paradigmatic control schemes, the ultrafast pump-dump control and the APLIP
(Adiabatic Passage by Light Induced Potentials) scheme, respectively.
L. González (B) · P. Marquetand · M. Richter
Institute of Theoretical Chemistry, University of Vienna, Währinger Str. 17, 1090 Vienna, Austria
e-mail: leticia.gonzalez@univie.ac.at
J. González-Vázquez · I. Sola
Departamento de Química Física I, Universidad Complutense, 28040 Madrid, Spain
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_7,
© Springer International Publishing Switzerland 2014
145
Ultrafast Laser-Induced Processes Described
by Ab Initio Molecular Dynamics
Leticia González, Philipp Marquetand, Martin Richter,
Jesús González-Vázquez, and Ignacio Sola
Abstract This chapter introduces theoretical methods that integrate the equations
of motion of electrons and nuclei in molecules, including all degrees of freedom
and all types of couplings. We are concerned with methods that treat the electronic
motion quantum-mechanically, by expanding the electronic wave function in a relatively small basis of eigenstates of the Hamiltonian, and the nuclear motion classically, as an ensemble of trajectories each unfolding on a single electronic state at a
given time, but allowing to switch between states. In particular, we focus on a quite
novel method called the SHARC (Surface-Hopping in the Adiabatic Representation
including arbitrary Couplings) scheme. The main novelty of SHARC consists in the
evaluation of the transition probability between electronic states, which is performed
by surface-hopping techniques in the adiabatic representation, essentially treating
on the same footing both non-adiabatic beyond Born-Oppenheimer transitions (intersystem crossing, internal conversion) and laser-induced crossings. The choice of
approximations and representation is particularly useful in evaluating the dynamics
when the laser field or non-adiabatic couplings are strong. In the chapter we show
examples of the performance of the scheme in two scenarios. In the first one, the
dynamics of the system is simulated starting in the electronic excited state assuming
an instantaneous excitation. In the second one, the interaction of the system with
an external laser field is explicitly considered. This approach is necessary when deactivation occurs during the laser excitation. Moreover, the explicit consideration
of the external field permits the use of quantum control schemes. We consider here
two limiting cases, the impulsive and the adiabatic time-evolution, represented by
two paradigmatic control schemes, the ultrafast pump-dump control and the APLIP
(Adiabatic Passage by Light Induced Potentials) scheme, respectively.
L. González (B) · P. Marquetand · M. Richter
Institute of Theoretical Chemistry, University of Vienna, Währinger Str. 17, 1090 Vienna, Austria
e-mail: leticia.gonzalez@univie.ac.at
J. González-Vázquez · I. Sola
Departamento de Química Física I, Universidad Complutense, 28040 Madrid, Spain
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_7,
© Springer International Publishing Switzerland 2014
145