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Introduction

The CRYSTAL program was jointly developed by the Theoretical Chemistry Group at the University of Torino and the Computational Materials Science group in STFC. CRYSTAL is an all electron, first principles simulation code implementing both Hartree Fock and density functional approaches in periodic systems. The wave functions are expanded in atom-centred Gaussian type orbitals (GTOs) providing a highly efficient and numerically precise solution with no shape approximation to the density or potential. Powerful screening techniques are used to exploit real space locality. The code may be used to perform consistent studies of the physical, electronic and magnetic structure of molecules, polymers, surfaces and crystalline solids.

Resources for CRYSTAL Users

The current release of CRYSTAL is CRYSTAL09 which is available from the CRYSTAL home page which also provides documentation and a number of resources for CRYSTAL users. There are very useful tutorials to learn how to use CRYSTAL that range for beginners to advanced and these are recommended for beginners use. Tutorials

New Functionality

A Technical Report on the implementation of the climbing-image nudged elastic band method within CRYSTAL is available here

For more information about CRYSTAL please contact crystal@dl.ac.uk or crystal@unito.it.

The DLVisualize Graphical User Interface

DL Visualize (DLV v3.0) provides an interface to CRYSTAL and a number of other materials simulation programmes. DLV supports geometry editing, job submission and the display of structures and properties.

Projects using CRYSTAL.

The computational material sciences group at STFC use CRYSTAL as essential software in order to carry out their research. Some examples of projects done using CRYSTAL are:
  • Magnetic coupling in V(TCNE)2

  • In this work, a model of V(TCNE)2 which satisfies a set of constraints based upon experimental evidence, is proposed. These constraints include (i) the observed stoichiometry, (ii) the suggested octahedral coordination for the metal ion, (iii) the presence of uncoordinated cyano groups, and (iv) the dimensionality of the material forming a periodic crystalline network of V atoms and TCNE molecules. Calculations of the structural, electronic, and magnetic properties of this model were performed using density functional theory as implemented in the CRYSTAL09 package.

  • Catalysis of the CCl2F2 - Dis mutation Reaction on AlF3.

  • HFCs are synthesised via halogen exchange reactions of CFCs and HF. Recently, there has been much interest in the use of aluminium fluoride (AlF3) as such a catalyst [1]. High surface area (HS) AlF3 has been shown to act as a very efficient catalyst for these reactions. In some cases it is even more effective than the widely used Swartz catalyst based on antimony pentafluoride. We used state of the art hybrid density functional theory to investigate the interaction of CCl2F2 with and to study the energetics of the proposed reaction pathway. The CRYSTAL program was used to perform these calculations. Reaction pathways for the dis mutation reaction were obtained using the nudged elastic band (NEB) algorithm, of which has recently been implemented in the CRYSTAL program. This algorithm requires the structures of the initial and final states of the transition pathway and an initial guess of the pathway.
    The reaction pathway for the catalysis of 2CCl2F2 + CCl3 on the surface of β-AlF3


  • Spin-qubits in Carbon Peapods.

  • Spin chains have the potential to provide the controlled interactions needed for quantum computing. Carbon is a candidate host for spin qubits because in 12C materials the small spin-orbit coupling and absence of hyperfine coupling ensures long spin coherence times. Carbon peapods, that is, single-walled carbon nanotubes (SWNT) containing fullerenes, have been proposed as particularly suitable spin chain systems. The fabrication of nanoscale electronic devices, such as field effect transistors, with carbon peapods containing various endohedral fullerenes is well established. When spin active metallic atoms such as Sc are incarcerated in a carbon cage, the system develops hybridized orbitals resulting in an unpaired electron delocalized across the fullerene cage potentially a near ideal qubit. The CRYSTAL code was used to perform calculations based on density functional theory (DFT).We find well-defined spin-1/2 qubits on the fullerenes, with strong evidence for a nearest-neighbour Heisenberg exchange interaction. In order to describe the influence on the spin-qubits localized on the fullerenes of propagating electrons or holes in the nanotube, it is necessary to go beyond DFT to a model which is capable of describing the low-energy charge-spin excitations of the system. We conjecture a generic Hubbard-Anderson model; which captures the Heisenberg exchange between spins along the fullerene chain and the Kondo exchange interaction between localized spins on the fullerenes and spins of propagating electrons or holes in the nanotube.


    CRYSTAL in Parallel

  • Massively Parallel CRYSTAL Calculations

  • The code implements Hartree Fock and density functional theory using a local Gaussian basis set providing for the accurate calculation of energy and forces for structural optimisation and a wide variety of material properties. The massively parallel implementation of CRYSTAL allows systems with ~1000 atoms per unit cell to be studied routinely on parallel computers. The two key computational steps are the evaluation of the Hamiltonian through the calculation of matrix element integrals and the solution of the Kohn Sham equations through diagonalisation of the Hamiltonian.

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