6 Tools

The directory tools contains a few tools that can be useful to build structures of solids, surfaces, ribbons, and nanowires. Moreover it contains some miscellaneous codes that give additional information on the internal conventions of thermo_pw or further process its output. Currently it contains the following programs:

• bravais_lattices.x tests the module lattices.f90 of the library. Pre- sently it can read three primitive lattice vectors of a Bravais lattice and find the ibrav code and the celldm parameters of the input lattice. It can also read two sets of primitive vectors and decide if they describe the same Bravais lattice. In the positive case it gives the orientation of one lattice with respect to the other. For an example of its use see tools_input/bravais_lattice.in.

• crystal_point_group.x is a crystal point group calculator. It can give several information about the crystallographic point groups, such as the list of symmetry operations, the product of two rotation matrices, the product table, the class structure, the character tables of the irreducible representations of the point group and of the double point group and the projective representations of the point group. It gives the list of subgroups and supergroups of a given group and the compatibility tables of a given group with its subgroups. It can also decompose the Kronecker product representations. Finally it can list the conjugate groups and calculate the intersection of two point groups. For an example of its use see tools_input/crystal_point_group.in.

• debye.x reads from input the Debye temperature and the number of atoms per unit cell and writes in a file the thermodynamic quantities (vibrational energy, free energy, entropy, and heat capacity) as a function of temperature computed using the Debye model. When the system has only one atomic type it writes the atomic B factor as a function of temperature computed using the Debye model. For an example of its use see tools_input/debye.in.

• elastic.x reads the elastic constants of a solid and computes the elastic compliances, the bulk modulus, and a few poly-crystalline averages. It uses the thermo_pw library so the output is the same. For an example of its use see tools_input/elastic.in.

• epsilon_tpw.x generalizes the routine epsilon.f90 of the QUANTUM ESPRESSO distribution. It calculates the complex dielectric constant of a solid as a function of the frequency for independent electrons using the LDA or GGA eigenvalues. It is limited to insulators, but supports norm-conserving, ultrasoft, and PAW pseudopotentials. It supports both scalar relativistic and fully relativistic pseudopotentials and it uses the point group symmetry of the solid to reduce the number of k-points. For an example of its use see example14.

• gener_nanowire.x reads a two dimensional (2D) Bravais lattice index and atomic coordinates an generates a sheet of type (m, n) . A sheet contained between the two vectors C= m a₁ + n a₂ and T = p a₁ + q a₂ can be also generated and wrapped about C in a nanotube form (a₁ and a₂ are the primitive lattices of the 2D Bravais lattice). For lattices that allow it, p and q can be determined automatically so that T is perpendicular to C. For an example of its use see tools_input/gener_nanowire.in.

• gener_2d_slab.x reads a two dimensional Bravais lattice index and atomic coordinates an generates an infinite ribbon perpendicular to G = m b₁ + n b₂ , where b₁ and b₂ are the primitive reciprocal lattice vectors of the 2D Bravais lattice. The number of rows of the ribbon, and the number of atoms per row are given as input variables. For an example of its use see tools_input/gener_2d_slab.in.

• gener_3d_slab.x reads a three dimensional Bravais lattice index and atomic coordinates and generates an infinite slab perpendicular to G = m b₁ + n b₂ + o b₃ , where b₁ , b₂ and b₃ are the primitive reciprocal lattice vectors of the Bravais lattice. The number of layers of each slab, and the size of the surface unit cell are given as input parameters. For an example of its use see tools_input/gener_3d_slab.in.

• hex_trig.x reads the values of a and c of the conventional hexagonal cell of a rhombohedral lattice (in Ångstrom), and gives as output the size a_r (in a.u.) and the cosine of the angle $\alpha$ of the rhombohedral cell. This information can be written in the input of pw.x for this type of cells. It is used to convert the structural information contained in a CIF file to the pw.x input.

• kovalev.x writes the correspondence between point group symmetry operations defined in the Kovalev tables and those used by QUANTUM ESPRESSO.

• mag_point_group.x gives a few information on the magnetic point groups.

• optical.x contains a few utilities for optical properties calculations. It transforms a complex dielectric constant into a complex index of refraction and computes the reflectivity or the absorption coefficient for cubic system. It converts also from energy of the photon in eV to the frequency in Hz or the wavelength in nm.

• pdec.x reads the temperature dependent elastic constants files calculated for several pressures and makes a plot of the elastic constants as a function of pressure at several temperatures.

• plot_sur_states.x reads the dump file produced by thermo_pw in a what='scf_2d_bands' calculation that contains the planar averages of all the states, and plots the states with the k point and the band numbers requested in input. For an example of its use see tools_input/plot_sur_ states.in.

• rotate_tensors.x applies a rotation to a tensor of rank 1, 2, 3, or 4 defined in a coordinate system 1 and finds the form of the tensor in a new coordinate system 2.

• space_groups.x gives several information on space groups. It can give the names of the space group given the number reported in the International Tables for Crystallography (ITA), or the number given one of the names, translate the names between different editions of the ITA tables or the Shönflies name. It gives the list of coset representatives of each space group and the list of symmorphic space groups. For an example of its use see tools_input/space_groups.in.

• supercell.x reads a three dimensional Bravais lattice index and the atomic coordinates of the atoms inside a unit cell and produces a supercell with n1 x n2 x n3 cells of the original unit cell or a supercell delimited by three arbitrary Bravais lattice vectors given in crystal or cartesian coordinates. For centered cells there is the option to consider n1 , n2 , and n3 for the primitive or for the centered Bravais lattices. The input unit cell can be specified also by giving the space group and the coordinates of the nonequivalents atoms. It can be useful to study defects or to calculate all the atomic positions starting from the space-group and the nonequivalent positions. It is also possible to give the input Bravais lattice by using ibrav=0 and the three principal vectors. In this case, before generating the supercell, the code rotates the Bravais lattice so that it has the same orientation of the vectors described in the thermo.pdf guide. For an example of its use see tools_input/supercell.in.

• test_colors.x produces a postscript file with the gnuplot colors that can be used in the plots.

• translate.x reads a set of atomic positions and a translation vector and translates the atomic positions. It can read also a rotation matrix and roto-translate the atomic positions.

• units.x writes on output the numerical constants used to write the guide units.pdf and equilibrium.pdf. It computes also the error associated to each conversion factor.

For a detailed description of the input variables please look at the beginning of the fortran sources of each code.