Research Activities

Implementation of software

The activity of the Group is mainly devoted to the implementation of computer software for the ab initio quantum-mechanical study of the properties of condensed matter. The general philosophy is to make the software developed available to the scientific community by periodically publishing well-tested and documented versions of the codes.

The CRYSTAL program

See the web site of the program, http://www.crystal.unito.it
(R. Dovesi, V. R. Saunders, C. Roetti, R. Orlando, B. Civalleri)

The CRYSCOR program

This is a new code, which calculates the correlation correction to HF wave-function and energy for periodic systems, starting from the HF results obtained by CRYSTAL, and using local-correlation techniques as developed by Meyer, Pulay, Werner, Sch├╝tz et al. for molecules. For the moment being, the treatment is restricted to the perturbative (MP2) case.
(http://www.cryscor.unito.it)
(C. Pisani, S. Casassa, R. Dovesi, L. Maschio)

The EMBED program

This code calculates electronic structure and energy of local defects in crystals in the HF approximation, using as an input information about the HF solution for the perfect host crystal obtained by CRYSTAL. The most recent version is EMBED01, related to CRYSTAL98.
(http://www.embed.unito.it/embed.html)
(C. Pisani, S. Casassa)

 

Characterization of condensed systems

  • Elastic Properties of Crystals
    An automated scheme has been developed in the CRYSTAL program for computing the elastic tensor of crystalline materials of any symmetry. Bulk and shear moduli, Poisson's ratio, Young's modulus and directional acoustic seismic wave velocities can be computed. The elastic anisotropy of a class of silicate garnets has been investigated. Elastic properties of several nanotubes have also been computed. Elastic properties of a variety of materials can be simulated. In particular, in the next future, we will investigate the effect of temperature and pressure on elastic properties of crystals.
    (A. Erba, A. Mahmoud, E. Albanese, B. Civalleri, R. Dovesi)
  • Piezoelectricity of Crystals
    The piezoelectric tensor of crystals of any space group of symmetry can now be computed with the CRYSTAL program. Piezoelectric response properties of low-temperature phases of perovskites such as SrTiO3 and BaTiO3, and Si/GeO2 solid solutions have recently been simulated. Piezoelectricity of nanotubes has been investigated as well. Piezoelectricity and electromechanical coupling can be computed on a number of systems of technological interest. The calculation of second-order piezoelectric constants will be implemented in the next future.
    (A. Erba, M. Rérat, E. Albanese, B. Civalleri, R. Dovesi)
  • Photoelasticity of Crystals
    An automated scheme has been devised and implemented in the CRYSTAL program for computing the photoelastic properties of crystals, which measure the variation of the refractive index as a function of the applied strain to the crystal lattice. Photoelastic constants have been computed for a variety of simple crystals and for BaTiO3. The electric field frequency dependence can also be explicitly taken into account. The present scheme will be extended to the calculation of the piezo-optic tensor and will be applied to the photoelastic characterization of materials of technological interest.
    (A. Erba, A. Mahmoud, R. Dovesi)
  • Effect of Pressure and Temperature
    A large variety of techniques is being developed in the CRYSTAL program for the inclusion of effect of pressure and temperature on several crystalline properties: electron charge density and X-ray structure factors, equilibrium structure, elastic constants, thermodynamical properties, etc. Some of these schemes will be implemented in the next future. Several applications will then be performed for the theoretical prediction of thermodynamical properties of crystals.
    (A. Erba, A. Mahmoud, M. Ferrabone, R. Dovesi)
  • Electron Momentum Distribution
    The analysis of the electron momentum distribution of several crystals has been performed theoretically, by comparing with accurate experimental Compton profiles. The effect of the adopted approximate Hamiltonian was found to be dramatic. Further studies on crystals of interest will be performed.
    (A. Erba, C. Pisani)
  • Local Electron correlation methods for periodic systems
    This research activity is oriented to the continuous improvement and extension of the CRYSCOR code, that allows the evaluation of correlation effects in crystalline materials at the second-order Moeller-Plesset (MP2) level within a local approach. After the first release of the code in 2010, the newest developments include the parallelization of the code, the implementation of numerical gradients for geometry optimization and the adoption of Orbital-Specific Virtuals (OSV) for the description of the unoccupied manifold.
    (L. Maschio, S. Casassa, S. Salustro)
  • Ab initio simulation of vibrational (Infrared and Raman) spectra of crystals
    The Coupled-Perturbed Hartree-Fock/Kohns-Sham (CPHF/KS) formalism implemented in CRYSTAL is used to evaluate analytically response properties, like the Born charges and the Raman tensor, that involve a mixed derivative of the total energy with respect to an external electric field and atomic displacements. Numerical differentiation with respect to atomic coordinates and with respect to wavevectors is entirely avoided as is the determination of crystal orbital coefficient derivatives with respect to nuclear displacements. We also apply the implemented algorithms to the simulation of Raman spectra of systems (garnets, silicates, MOFs) for which the simulation is proving to be an invaluable tool to complement the experiment in the assignment of Raman peaks.
    (L. Maschio, M. De La Pierre, R. Dovesi, R. Orlando, S. Salustro)
  • Molecular crystals
    We use recently developed DFT functionals, including doubly hybrid functionals, as well as the periodic local MP2 method implemented in CRYSCOR to study properties of molecular crystals, like their cohesive energy and the relative stability of their polymorphs.
    (B. Civalleri, L. Maschio)
  • Nanostructured and Graphene-based materials
    In this research activity materials derived from graphene and carbon nanotubes (CNNTs) are studied. Their structural, electronic, dielectric and vibrational properties are simulated at an ab initio level using hybrid functionals. Novel graphene phases are proposed, that feature several types of defects (vacancies, heteroatomic substitutions). Finally, the interaction of Graphene with different substrates and/or gas-phase molecules is investigated.
    (R. Dovesi, B. Civalleri, L. Maschio, M. De La Pierre, M. Lorenz, J. Baima)
  • Ab-initio modeling of Metal Organic Frameworks
    Metal-Organic Frameworks (MOFs) are a new class of materials that in the last decade has seen a paramount growth and are expected to play a huge impact in the development of next-generation technologies. They consist of inorganic nodes (i.e. a metal ion or a cluster) connected through organic ligands that act as linkers to form a porous three-dimensional framework. The combination of different nodes and linkers makes MOFs very versatile materials with interesting and promising applications in many fields, including: gas adsorption, catalysis and photo-catalysis, drug delivery, sensing, nonlinear optics. In the last years, a throughout characterization of the structural, electronic, vibrational, elastic properties of different families of MOFs has been carried out, along with the investigation of their adsorption capacity. In collaboration with experimentalists, we studied the adsorption capabilities of MOF-74(Mg,Ni,Zn) and Ni-BTP towards small molecules like CO, CO2, N2, .. We are currently investigating the adsorption properties of the so-called giant MOFs (also know as mesoporous MOFs) in particular of MIL-100. Along with small molecules, selected drugs will be considered to better understand the properties of MIL-100 as a nano carrier material for drug delivery. This latter work has been recently funded with a PRACE grant. Defects in the zirconium MOF UiO-66 are also under investigation to shed some light on the synthesis of UiO-66 and its stability.
    (B. Civalleri, M. Ferrabone, E. Albanese, L. Maschio, S. Casassa)
  • Hydrogen storage materials
    Light-weight metal boron hydrides (MBH) (e.g. Mg, Ca, ..) are under investigation as potential hydrogen storage materials. The research activity is focused on the ab-initio prediction of the decomposition energy of the MBHs to tune their thermodynamic stability with respect to the release of molecular hydrogen in order to reach the target value of about 30 kJ/mol per H2 molecule. To do that, mixed metal boron hydrides have been studied by exploring Mg/Zn solid solutions. Nanostructuring and confinement of MBH in carbon scaffolds have also been investigated through model systems such as small clusters of MBH adsorbed on graphene. In addition, the role of additives (e.g. transition metals) on the stability of MBH is under investigation for both bulk and surfaces to understand how additives can modify the decomposition pathways. Fundings are acknowledged from EC FP-7.
    (B. Civalleri, R. Dovesi, E. Albanese)
  • Ice structures
    After designing pseudo-disordered models of ordinary ice and characterizing in this way its bulk and surface properties, current research activity is devoted to ice vibrational properties and to ice clathrates.
    (S. Casassa, A. Mahmoud)
  • Epitaxial oxide/metal films
    Epitaxial overlayers of MgO or NiO on Ag(001) have been characterized by using slab models. Attention is being given to the early (sub-monolayer) stages of the film growth.
    (A. Ferrari)