Interaction between fullerene-wheeled nanocar and gold substrate: A DFT study

https://doi.org/10.1016/j.physe.2016.05.029Get rights and content

Highlights

  • Ab initio DFT calculations were used for interaction of nanocar with Au surface.

  • Full structural optimization was performed for several possible active sites.

  • Electronic structure of the energetically favorable complexes was analyzed.

  • The binding energy of nanocar/Au was determined to be −217.45 kcal/mol.

  • DFT-MD simulation was performed for a C60 on gold surface at ambient condition.

Abstract

Since the successful synthesis of nanocar and its surprising movement on the gold surface, several theoretical investigations have been devoted to explain the interaction properties as well as its movement mechanism on the substrate. All of them failed, however, to gain a clear theoretical insight into the respected challenges because of the weak computational methods implemented for this complex system including heavy metal atoms and giant size of the whole system. In this work, we have investigated the adsorption of fullerene-wheeled nanocar onto a Au (1 1 1) substrate using the comprehensive first-principles density functional theory (DFT) simulations. The binding energy between the nanocar and Au (1 1 1) surface was determined to be −9.43 eV (−217.45 kcal/mol). The net charge transfer from the nanocar to the gold substrate was calculated to be about 9.56 electrons. Furthermore, the equilibrium distances between the Au surface and the C60 molecule and nanocar chassis were estimated to be 2.20 Å and 2.30 Å, respectively. The BSSE correction was also considered in the binding energy estimation and the result show that the BSSE correction significantly affects the calculated binding energy for such systems.

Finally, we have performed ab initio molecular dynamics simulation for a single C60 fullerene on the gold surface at room temperature. Our first-principles result shows that ambient condition affect remarkably on the adsorption property of fullerene on the gold surface. We also observed that the C60 fullerene wheel slips by approximately 3.90 Å within 5 ps of simulation time at 300 K.

Introduction

Recent efforts have been focused on synthesizing artificial molecular machines that convert chemical, thermal, or light energy into useful mechanical work at the molecular level and to ultimately construct molecular assemblies via a bottom-up approach [1], [2], [3], [4], [5], [6]. One important class of molecular machines that accomplish directed molecular motion and transportation is nanocars [7]. Such molecular objects consist of two to four wheels chemically coupled to a planar chassis [8]. Fullerenes (C60) appear to make more suitable wheels than triptycene for surface translations because of their spherical shape and good physical/chemical properties. First-generation nanocars consisted of an oligo (phenylene ethynylene) alkynyl chassis connected to four fullerene wheels (fullerene-wheeled nanocar) and were studied at the single-molecule level [9]. Scanning tunneling microscopy (STM) imaging studies demonstrated that these molecular structures are motionless on the surface at room temperature (300 K) due to strong charge transfer interactions between the fullerenes and gold surface; however, increasing the temperature causes translational motion parallel to the substrate [10], [11]. The experimental development and analysis of fullerene-wheeled nanocars have stimulated various theoretical methods for understanding their detailed mechanisms and dynamics. Current theoretical investigations of artificial molecular machines primarily rely on molecular dynamics (MD) computer simulations [8], [12]. The most challenging aspect of these methods is accurately describing the interactions between the nanocar and metal substrate.

In this study, we have investigated the interactions between a fullerene-wheeled nanocar and Au (1 1 1) substrate (Au/nanocar system) using the first-principles density functional theory (DFT) method for the first time. We selected the Au (1 1 1) substrate to simulate the realistic model of gold crystals as determined by scanning tunneling microscopy (STM) [1] and also to compare the present DFT-LDA calculations with the previous studies with the dispersion corrected DFT-PBE calculations. For this propose and for simplicity the fullerene-wheeled nanocar was divided into two parts, the fullerene wheel and the chassis. We have estimated the binding energy, geometrical parameters, and charge transfer between the nanocar and gold substrate, accordingly. Moreover, we have considered the fullerene wheel position on the gold surface at room temperature by using DFT-based molecular dynamics (DFT-MD) to examine the effect of temperature on the binding nature as well as nanocar position on the substrate. In addition, we have considered the basis set superposition error (BSSE) which may influence significantly the binding energy of such systems and corrected the estimation of binding energy, accordingly.

Section snippets

Computational details

Our calculations for the fullerene wheels and chassis adsorbed on a Au (1 1 1) surface were performed via the first-principles DFT framework implemented using the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code [13]. For all calculations, we used the local density approximation (LDA) within the Ceperely-Alder (CA) form [14]. A split-valence double-ζ basis set of localized numerical atomic orbitals was used with an energy shift of 55 meV and a split norm of 0.3

Results and discussion

To investigate the adsorption of the fullerene-wheeled nanocar on the gold substrate, we divided the optimized nanocar into a fullerene wheel and chassis and then separately studied the adsorption of each part on the Au (1 1 1) surface. A full structural optimization was first performed on the fullerene, nanocar chassis and Au (1 1 1) substrate, separately. The optimized structures and geometrical parameters of the chassis are shown in Fig. 1.

To determine a favorable position for the C60

Conclusion

In summary, we investigated the interaction between a fullerene-wheeled nanocar and Au (1 1 1) substrate using the first-principles DFT method. Our results indicated that the C60 fullerene prefer to be adsorbed on the Au (1 1 1) surface with a binding energy of −1.54 eV at zero K. We have also evaluated the effect of BSSE correction on the binding energy value and the result show that the BSSE correction significantly affect on the energy estimation (−1.85 eV without the BSSE correction). The

Acknowledgment

The authors gratefully acknowledge the resources of the High Performance Cluster Computing Centre, Pharmaceutical Sciences Branch, Islamic Azad University, Tehran.

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