Ab Initio Modelling of Nanodiamond

Significant Achievements, Anticipated Outcomes and Future Work

Major advances in this project in this year have been investigating dopants [1,2], two-dimensional structures [3] and in visualizing electronic structures [4]. This is whilst extending some of previously the successful work on zero- and one-dimensional carbon based systems [5,6] .A review on these methods appeared as an invited chapter in "Handbook of Theoretical and Computational Nanotechnology", editors M. Rieth, W. Schommers, American Scientific Publishers [6].

The work on dopants enables us to predict which dopants would form stable structures in nano-diamonds which is important since atomic dopants are used to modify the properties of materials e.g. their optical and electrical characteristics, for use in various applications. The structures which result must be stable in order for such procedures to produce useful materials. Here it was shown that some atoms may be successfully incorporated into a diamond-like structure e.g. N but some do not lead to stable structures e.g. O. Both nano-clusters (zero-dimensional nano-diamonds) [1,2] and diamond nano-wires (one-dimensional nano-diamond) were investigated [2].

The investigation of two-dimensional systems [3] showed some surprising results. It is often assumed that for 2-D graphene sheets the stable form on this length scale are nano-tubes and that flat sheets will naturally curl up to form these nano-tubes. However, we showed that flat graphene sheets even when heated are very stable and don't readily curl into nano-tubes. Subsequently, we showed that this is because both flat sheets of graphene and nanotubes have similar energies and are both relatively stable. Also there is an energy barrier which has to be overcome in order to transform from sheets to tubes and vice versa and this involves considerable energy. Thus, both stable flat sheets and stable tubes should exist as has been shown to experimentally.

It is often difficult to visualise the electronic structure and, hence, the type of bonding involved in a structure especially if it is a nano-structure and consists of carbon atoms. This is because such small structures involve the co-existence of a variety of bond lengths and bonding arrangements. We, thus, developed a method to visualise the type of bonding involved in nano-structures which was able to clearly differentiate between different types of bonding in carbon nano-structures [4].

Work to improve ab-initio density functional theories (DFT) to give an adequate description of van der Waals interactions using Quantum Monte Carlo methods, Hartree-Fock theory and DFT in also continuing.

Data Sources, Curation Techniques, Data Access Policy and Method

Not Applicable

Computational Techniques Used

The calculations in this project are performed by:
CRYSTAL2003 which enables both Hartree-Fock (HF) and Density Functional Theory (DFT) computations to be performed on molecules, polymers, surfaces and solids using Gaussian basis sets.

VASP which enables DFT to be performed on molecules, polymers, surfaces and solids using a plane basis set.

CASINO which uses the output of CRYSTAL2003 as input and performs QMC calculations both of a variational type (VMC) or a diffusional type (DMC). This enables more accurate prediction of the absolute stability of some systems of interest. It is also essential to use to describe certain types of interactions e.g. those involving van der Waals and hydrogen bond interactions which are important in some systems.

In-house codes which are being developed to calculate free energies of nano-structures. Due to large memory resources and the large amount of computer time required and APAC-NF is the only system in Australia equipped to run the large calculations required to complete this project.

Publications, Awards and External Funding

External Funding and Awards

ARC Discovery Grant, DP0556439, I.K. Snook, S.R. Russo, R. Needs and M.D. Towler, "Accurate quantum modeling of the van der Waals interaction and its application to molecular physisorption onto surfaces", 2005-2007.

Publications

1. A.S. Barnard, S.P. Russo and I.K. Snook, “First-Principles Modelling of Dopants in C₂₉ and C₂₉H₂₄ Nanodiamonds: Part II”. J. Phys. Chem. B, 109 11991-11995 (2005).
2. A.S. Barnard, S.P. Russo and I.K. Snook, “Simulation and Bonding of Dopants in Nanocrystalline Diamond”. Invited review for special issue of J. Nanosci. Nanotech, 5 (9) 1395–1407 (2005).
3. Ian Snook, Amanda Barnard, Salvy Russo, Ryan Springal and Jhan Srbinovsky, “Simulating Nano-Carbon Materials”. Molecular Simulation, 31 495 – 504 (2005).
4. A.S. Barnard, S.P. Russo and I.K. Snook, “Visualizing Hybridization in Nanocarbon Systems”. J. Comp. Theo. Nanosci., 2 68 (2005).
5. A.S. Barnard, S.P. Russo and I.K. Snook, “Modeling of Stability and Phase Transformations in Quasi-Zero Dimensional Nanocarbon Systems”. J. Comp. Theo. Nanosci., 2 1-22 (2005).
6. A.S. Barnard, S. P. Russo and I.K. Snook, “Modeling of Stability and Phase Transformations in 0 and 1 Dimensional Nanocarbon Systems”. Invited chapter for "Handbook of Theoretical and Computational Nanotechnology", editors M. Rieth, W. Schommers, American Scientific Publishers, 2005.