The actual rapid progress in computers stimulates the development of the mathematical models which are aimed to describe the real processes in the nature. Upgrading of such models involves, as a rule, taking account of more factors, as well as their dynamics and interaction. As a result, sometimes one obtains a model involving a great number of obscure parameters, a model within which it is already impossible to select the main factors determining the phenomenon under study.
Much the same situation is now in the field of the numerical modeling of crystal lattice dynamics. The variety of methods to calculate the electronic energy of many electron systems have been developed in quantum mechanics (or more precisely, in «quantum chemistry»). In principle, they allow us to construct the adiabatic potential surface of a crystal lattice and to calculate all the dynamical properties. However, the success of such an approach depends on a lucky choice of the quantum- chemical approximation (the basis set, the parametrization of the local density functional, etc.). Besides, the self-consistent solution of a many electron problem for a crystal with dozens of atoms in the unit cell is still beyond the potentiality of modern programs and computers. The theoretical and computing difficulty grows essentially when one tries to account the anharmonic effects and to model the thermal properties.
At the same time, recent publications give us some examples when it was possible, by using a simple but reasonably chosen analytical approximation of the adiabatic potential, to obtain a comprehensive description of the dynamical properties of complex crystals, including such complicate phenomena as phase transitions and polymorphism. Successfulness of these potential models is based on an appropriate combination of the quantum and classical methods. First, the electronic energy of the isolated clusters (which serve to model the analogous crystal fragments) is calculated by a non- empirical quantum-mechanical method. Then by means of numerical interpolation, the analytic interatomic potentials are drown. Finally, these potentials are used to simulate the lattice dynamics. The conceptual simplicity of this approach raises the numerical efficiency as well as facilitates the interpretation of the obtained results. Every term within such a potential model corresponds to the certain type of physical interaction, so it become possible, by revealing their relative roles, to answer not only the question «How?», but also «Why?». Actually, there are several programs to simulate the dynamical property of crystals within a potential models (Unisoft, Climax, Molecular Simulations etc.). Each of them has the advantages and shortcomings (completeness, convenience of use, graphics etc.). We have tried to take into account disadvantages of other programs, and to develop the program package LADY (LAttice DYnamics toolkit), which allows you, having determined a potential model, to simulate different properties of a crystal, including:
- crystal structure
- dynamical properties - phonon states, elastic and piezoelectric constants
- IR, Raman and neutron scattering spectra
- thermodynamic properties - temperature and pressure dependence of the crystal structure and all
the above listed dynamical properties
LADY incorporates many widely used potential models.
LADY accomplishes an automatic account of the crystal symmetry for both the crystal structure and the phonon states.
LADY is applicable for a crystal of arbitrary chemical and spatial constitution.
LADY includes a graphics routines which allow you to visualize crystal structure, the calculated eigenvectors, phonon dispersion relations, DOS and many other calculated dependencies.
LADY has the user-friendly interface.
Please visit our About page to see the set of screenshots.
We provide only windows binary version at the moment. You can grab it here: http://sourceforge.net/projects/ladytool/files/win-old-release/lady_win.zip