First-Principles Simulations of Chemical Reactions in an HCl Molecule Embedded inside a C or BN Nanotube Induced by Ultrafast Laser Pulses

Abstract

We show by first-principles simulations that ultrafast laser pulses induce different chemical reactions in a molecule trapped inside a nanotube. A strong laser pulse polarized perpendicular to the tube axis induces a giant bond stretch of an encapsulated HCl molecule in semiconducting carbon nanotube or in a BN nanotube. Depending on the initial orientation of the HCl molecule, the subsequent laser-induced dynamics is different: either complete disintegration or rebonding of the HCl molecule. Radial motion of the nanotube is always observed and a vacancy appears on the tube wall when the HCl is perpendicular to the tube axis. The photophysical and photochemical properties of single-walled carbon nanotubes (SWCNTs) have attracted a lot of interest recently [1-4] almost 20 years after the identification of chiral structures of carbon nanotubes (CNTs) [5,6]. The nanometer space inside SWCNTs has been used to fill nanotubes with metals [7] and molecules [8][9][10]. The rich variety of chemical properties and the modifications of those induced by the tube-wall confinement have opened a new avenue of research linked to the one-dimensional nanoconfined chemistry. SWCNTs could be used to control molecular self-assembly which is a key in nanotechnology. Photochemistry in those confined spaces was observed for photoharvesting chromophores inside CNTs [11] and their carrier dynamics were analyzed by optical spectroscopy [12]. Understanding the confinement effect in the photophysics and photochemistry of encapsulated molecules is of fundamental and practical interest.In this Letter, we propose using a short and intense laser pulse to control the photochemistry of molecules inside carbon and BN nanotubes. The benefit of trapping molecules inside CNTs is to increase the cross section of the photoirradiation compared to those in gas phase. To theoretically simulate the photochemical dynamics in such nanospace we should take into account depolarization [13][14][15] or enhancement [16] of the optical electric field (E field) depending on the optical frequency. A firstprinciples approach is needed, which has motivated the work in the Letter. We chose an HCl molecule as a test case and found significant expansion or dissociation of the molecule depending on the molecular orientation inside an (8,0) carbon nanotube or inside an (8,0) BN nanotube under irradiation of strong and short laser pulse.Photochemical reactions can be treated within timedependent density functional theory (TDDFT) [17].TDDFT using the simplest local-density approximation (TDLDA) was applied to study the dynamics of metal clusters and isolated molecules [18,19] in the presence of a strong laser pulse. We extended this type of TDLDA approach to photochemistry in the nanospace inside SWCNTs. Dynamics of the HCl molecule inside semiconducting nanotubes was calculated under the pulse laser with wavelength of 800 nm and the full width at half maximum as 2 fs. These conditions make duration time of the pulse only 4 fs and make the pulse shape strongly asymmetric in ...

Laser-induced preferential dehydrogenation of graphane

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Electron dynamics with real‐time time‐dependent density functional theory

“…Figure shows the evolution of charge transfer for a triad molecule relevant to photovoltics where free evolution of the nuclei result in significant charge transfer . In addition, this method is able to model dissociation and fragmentation processes, as well as collisions that transform kinetic energy of nuclei into electronic excitations, and has been applied to systems as large as fullerenes and nanotubes . Because of the large difference in masses for electrons and nuclei, the propagation of electronic and nuclear motion is generally carried out with two different time steps, with the nuclear time step usually two or three orders of magnitude greater than the electronic time step.…”

Efficient electron dynamics with the planewave-based real-time time-dependent density functional theory: Absorption spectra, vibronic electronic spectra, and coupled electron-nucleus dynamics

“…40 Numerical methods to solve the above TDKS equation have been studied based on various quantum computational codes. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] However, the details are quite different depending on the basis sets. In this paper, we focus on the PW-based code.…”

“…Sugino and Miyamoto have developed PW-based electron dynamics program using the self-consistent ST 4 operator, 16 and have studied the behavior of electron propagation in the condensed matter system. 18,19 Yabana et al and Castro et al have solved the RT-TDDFT in numerical grids, and obtained successful absorption spectra of several molecules. [12][13][14][15] For the case of atomic orbital basis sets, many researchers have studied excited state properties by using their house-made real-time electron dynamics program.…”

“…[4][5][6][7][8][9][10][11] However, it is limited to investigate the response of electron density beyond the linear response, according to the applied perturbation, and can be described regardless of the strength of the perturbation. To this end, the real-time time-dependent density functional theory (RT-TDDFT), [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] a real-time approach in TDDFT regime, 27 is proposed to investigate the "real" electron dynamics according to the applied external field.…”