# The STRU file

## Examples

The `STRU`

file contains the information about the lattice geometry, the name(s) and/or location(s) of the pseudopotential and numerical orbital files, as well as the structural information about the system. We supply two ways of specifying the lattice geometry. Below are two examples of the `STRU`

file for the same system:

### No latname

For this example, no need to supply any input to the variable `latname`

in the INPUT file. (See input parameters.)

```
ATOMIC_SPECIES
Si 28.00 Si_ONCV_PBE-1.0.upf upf201 // label; mass; pseudo_file
NUMERICAL_ORBITAL
Si_gga_8au_60Ry_2s2p1d.orb //numerical_orbital_file
LATTICE_CONSTANT
10.2 // lattice scaling factor (Bohr)
LATTICE_VECTORS
0.5 0.5 0.0 // latvec1
0.5 0.0 0.5 // latvec2
0.0 0.5 0.5 // latvec3
ATOMIC_POSITIONS
Direct //Cartesian or Direct coordinate.
Si // Element type
0.0 // magnetism(Be careful: value 1.0 refers to 1.0 bohr mag, but not fully spin up !!!)
2 // number of atoms
0.00 0.00 0.00 0 0 0
0.25 0.25 0.25 1 1 1
```

### latname fcc

We see that this example is a silicon fcc lattice. Apart from setting the lattice vectors manually, we also provide another solution where only the Bravais lattice type is required, and the lattice vectors will be generated automatically. For this example, we need to set `latname="fcc"`

in the INPUT file. (See input parameters.) And the `STRU`

file becomes:

```
ATOMIC_SPECIES
Si 28.00 Si_ONCV_PBE-1.0.upf // label; mass; pseudo_file
NUMERICAL_ORBITAL
Si_gga_8au_60Ry_2s2p1d.orb //numerical_orbital_file
LATTICE_CONSTANT
10.2 // lattice scaling factor (Bohr)
ATOMIC_POSITIONS
Direct //Cartesian or Direct coordinate.
Si // Element type
0.0 // magnetism
2 // number of atoms
0.00 0.00 0.00 0 0 0//the position of atoms and other parameter specify by key word
0.25 0.25 0.25 1 1 1
```

The LATTICE_VECTORS section is removed.

## Structure of the file

The `STRU`

file contains several sections, and each section must start with a keyword like `ATOMIC_SPECIES`

, `NUMERICAL_ORBITAL`

, or `LATTICE_CONSTANT`

, etc. to signify what type of information that comes below.

ATOMIC_SPECIES

This section provides information about the type of chemical elements contained the unit cell. Each line defines one type of element. The user should specify the name, the mass, and the pseudopotential file used for each element. The mass of the elment is only used in molecular dynamics simulations. For electronic-structure calculations, the actual mass value isn’t important. In the above example, we see information is provided for the element

`Si`

:Si 28.00 Si_ONCV_PBE-1.0.upf upf201 // label; mass; pseudo_file; pseudo_type

Here

`Si_ONCV_PBE-1.0.upf`

is the pseudopotential file. When the path is not specified, the file is assumed to be located in work directory. Otherwise, please explicitly specify the location of the pseudopotential files.After the pseudopotential file,

`upf201`

is the type of pseudopotential. There are five options:`upf`

(.UPF format),`upf201`

(the new .UPF format),`vwr`

(.vwr format),`blps`

(bulk-derived local pseudopotential), and`auto`

(automatically identified). If no pseudopotential type is assigned, the default value is`auto`

, and the pseudopotential type will be automatically identified.Different types of pseudopotentials can be used for different elements, but note that the XC functionals assigned by all pseudopotentials should be the same one. If not, the choice of XC functional must be set explicitly using the dft_functional keyword.

Common sources of the pseudopotential files include:

NUMERICAL_ORBITAL

Numerical atomic orbitals are only needed for

`LCAO`

calculations. Thus this section will be neglected in calcultions with plane wave basis. In the above example, numerical atomic orbitals is specified for the element`Si`

:Si_gga_8au_60Ry_2s2p1d.orb //numerical_orbital_file

‘Si_gga_8au_60Ry_2s2p1d.orb’ is name of the numerical orbital file. Again here the path is not specified, which means that this file is located in the work directory.

Numerical atomic orbitals may be downloaded from the official website.

LATTICE_CONSTANT

The lattice constant of the system in unit of Bohr.

LATTICE_VECTORS

The lattice vectors of the unit cell. It is a 3by3 matrix written in 3 lines. Please note that

*the lattice vectors given here are scaled by the lattice constant*. This section must be removed if the type Bravais lattice is specified using the input parameter`latname`

. (See input parameters.)LATTICE_PARAMETERS

This section is only relevant when

`latname`

(see input parameters) is used to specify the Bravais lattice type. The example above is a fcc lattice, where no additional information except the lattice constant is required to determine the geometry of the lattice.However, for other types of Bravais lattice, other parameters might be necessary. In that case, the section

`LATTICE_PARAMETERS`

must be present. It contains**one single line**with some parameters (separated by blank space if multiple parameters are needed), where the number of parameters required depends on specific type of lattice.The three lattice vectors v1, v2, v3 (in units of lattice constant) are generated in the following way:

latname = “sc”: the LATTICE_PARAMETERS section is not required:

v1 = (1, 0, 0) v2 = (0, 1, 0) v3 = (0, 0, 1)

latname = “fcc”: the LATTICE_PARAMETERS section is not required:

v1 = (-0.5, 0, 0.5) v2 = (0, 0.5, 0.5) v3 = (-0.5, 0.5, 0)

latname = “bcc” : the LATTICE_PARAMETERS section is not required:

v1 = (0.5, 0.5, 0.5) v2 = (-0.5, 0.5, 0.5) v3 = (-0.5, -0.5, 0.5)

latname = “hexagonal” : One single parameter is required in the LATTICE_PARAMETERS section, being the ratio between axis length c/a. Denote it by x then:

v1 = (1.0, 0, 0) v2 = (-0.5, sqrt(3)/2, 0) v3 = (0, 0, x)

latname = “trigonal” : One single parameter is required in the LATTICE_PARAMETERS section, which specifies cosγ with γ being the angle between any pair of crystallographic vectors. Denote it by x then:

v1 = (tx, -ty, tz) v2 = (0, 2ty, tz) v3 = (-tx, -ty, tz)

where tx=sqrt((1-x)/2), ty=sqrt((1-x)/6), and tz=sqrt((1+2x)/3).

latname = “st” (simple tetragonal) : One single parameter is required in the LATTICE_PARAMETERS section, which gives ratio between axis length c/a. Denote it by x then:

v1 = (1, 0, 0) v2 = (0, 1, 0) v3 = (0, 0, x)

latname = “bct” (body-centered tetragonal) : One single parameter is required in the LATTICE_PARAMETERS section, which gives ratio between axis length c/a. Denote it by x then:

v1 = (0.5, -0.5, x) v2 = (0.5, 0.5, x) v3 = (-0.5, -0.5, x)

latname = “so” (simple orthorhombic) : Two parameters are required in the LATTICE_PARAMETERS section, which gives ratios between axis length b/a and c/a. Denote them by x, y then:

v1 = (1, 0, 0) v2 = (0, x, 0) v3 = (0, 0, y)

latname = “baco” (base-centered orthorhombic) : Two parameters are required in the LATTICE_PARAMETERS section, which gives ratios between axis length b/a and c/a. Denote them by x, y then:

v1 = (0.5, x/2, 0) v2 = (-0.5, x/2, 0) v3 = (0, 0, y)

latname = “fco” (face-centered orthorhombic) : Two parameters are required in the LATTICE_PARAMETERS section, which gives ratios between axis length b/a and c/a. Denote them by x, y then:

v1 = (0.5, 0, y/2) v2 = (0.5, x/2, 0) v3 = (0, x/2, y/2)

latname = “bco” (body-centered orthorhombic) : Two parameters are required in the LATTICE_PARAMETERS section, which gives ratios between lattice vector length b/a and c/a. Denote them by x, y then:

v1 = (0.5, x/2, y/2) v2 = (-0.5, x/2, y/2) v3 = (-0.5, -x/2, y/2)

latname = “sm” (simple monoclinic) : Three parameters are required in the LATTICE_PARAMETERS section, which are the ratios of lattice vector length b/a, c/a as well as the cosine of angle between axis a and b. Denote them by x, y, z then:

v1 = (1, 0, 0) v2 = (x*z, x*sqrt(1-z^2, 0) v3 = (0, 0, y)

latname = “bacm” (base-centered monoclinic) : Three parameters are required in the LATTICE_PARAMETERS section, which are the ratios of lattice vector length b/a, c/a as well as the cosine of angle between axis a and b. Denote them by x, y, z then:

v1 = (0.5, 0, -y/2) v2 = (x*z, x*sqrt(1-z^2), 0) v3 = (0.5, 0, y/2)

latname = “triclinic” : Five parameters are required in the LATTICE_PARAMETERS section, namely the ratios b/a, c/a; the cosines of angle ab, ac, bc. Denote them by x,y,m,n,l, then:

v1 = (1, 0, 0) v2 = (x*m, x*sqrt(1-m^2), 0) v3 = (y*n, y*(l-n*m/sqrt(1-m^2)), y*fac)

where \(fac=\frac{\sqrt{1+2*m*n*l-m^2 -n^2 -l^2 }}{\sqrt{1-m^2}}\)

ATOMIC_POSITIONS

This section specifies the positions and other information of individual atoms.

The first line signifies method that atom positions are given, the following options are supported:

`Direct`

: coordinates of atom positions below would in fraction coordinates.`Cartesian`

: Cartesian coordinates in unit of ‘LATTICE_CONSTANT’.`Cartesian_au`

: Cartesian coordinates in unit of Bohr, same as setting of`Cartesian`

with`LATTICE_CONSTANT`

= 1.0 .`Cartesian_angstrom`

: Cartesian coordinates in unit of Angstrom, same as setting of`Cartesian`

with`LATTICE_CONSTANT`

= 1.889726125457828 .`Cartesian_angstrom_center_xy`

: Cartesian coordinates in unit of Angstrom, with Direct coordinate (0.5, 0.5, 0.0) as reference.`Cartesian_angstrom_center_xz`

: Cartesian coordinates in unit of Angstrom, with Direct coordinate (0.5, 0.0, 0.5) as reference…`Cartesian_angstrom_center_yz`

: Cartesian coordinates in unit of Angstrom, with Direct coordinate (0.0, 0.5, 0.5) as reference…`Cartesian_angstrom_center_xyz`

: Cartesian coordinates in unit of Angstrom, with Direct coordinate (0.5, 0.5, 0.5) as reference…

The following three lines tells the elemental type (

`Fe`

), the initial magnetic moment (`1.0`

), and the number of atoms for this particular element (`2`

) repsectively. Notice this magnetic moment will be a default value for every atom of this type but will be overrided if one define it for each atom by keyword(see below).The last two lines in this example are the coordinates of atomic positions. There are three numbers in each line, which specifies the atomic positions, following by other parameters marked by keywords.

Several other parameters could be defined after the atom position using key word :

`m`

or NO key word: three numbers, which take value in 0 or 1, control how the atom move in geometry relaxation calculations. In example below, the numbers`0 0 0`

following the coordinates of the first atom means this atom are*not allowed*to move in all three directions, and the numbers`1 1 1`

following the coordinates of the second atom means this atom*can*move in all three directions.`v`

or`vel`

or`velocity`

: set the three components of initial velocity of atoms in geometry relaxation calculations(e. g.`v 1.0 1.0 1.0`

).`mag`

or`magmom`

: set the start magnetization for each atom. In colinear case only one number should be given. In non-colinear case one have two choice:either set one number for the norm of magnetization here and specify two polar angle later(e. g. see below), or set three number for the xyz commponent of magnetization here (e. g.`mag 0.0 0.0 1.0`

). Note that if this parameter is set, the initial magnetic moment setting in the second line will be invalid.`angle1`

: in non-colinear case, specify the angle between c-axis and real spin, in angle measure instead of radian measure`angle2`

: in non-colinear case, specify angle between a-axis and real spin in projection in ab-plane , in angle measure instead of radian measuree.g.:

Fe 1.0 2 0.0 0.0 0.0 m 0 0 0 mag 1.0 angle1 90 angle2 0 0.5 0.5 0.5 m 1 1 1 mag 1.0 angle1 90 angle2 180