Calculations using riper module require the control file and starting orbitals generated using define. DFT method needs to be specified in the $dft data group. All pure GGA functionals are supported for periodic calculations. For molecular case hybrid functionals are also available. Moreover, an auxiliary basis defined in the data group $jbas is required. For periodic calculations additional keywords specifying the system periodicity and number of k-points (if used) are to be manually added. Finally the $riper group containing all options specific to this module (including the preconditioned conjugate gradient options) needs to be created. The input preparation steps are summarized below. More detailed informations about all options are in section 21.2.7.

- Run define: in the geometry menu choose C1 symmetry. Create data groups $dft and $jbas using dft and ri, respectively, in the general menu.
- For periodic calculations specify system dimensionality by adding the keyword $periodic n and cell parameters with the keyword $cell. A 3D unit cell needs to be defined regardless of the system periodicity. Dimensions of the unit cell must be large enough to enclose all atoms specified in the coord data group.
- When k-points are used specify their number using keyword $kpoints.
- Create the $riper data group.

riper > riper.out &

$periodic 3

$cell

18.5911 16.5747 16.5747 90. 90. 90.

$kpoints

nkpoints 3 3 3

$riper

# CFMM control options

northol 5

lmaxmom 20

nctrgt 10

wsicl 3.0

epsbext 1.0d-9

locmult on

locmomadd 2

pqmatdiag off

pqsingtol 1.0d-8

# PCG control options

lpcg off

lcfmmpcg on

lmxmompcg 20

pcgtol 1.0d-9

pcgtyp sp

$cell

18.5911 16.5747 16.5747 90. 90. 90.

$kpoints

nkpoints 3 3 3

$riper

# CFMM control options

northol 5

lmaxmom 20

nctrgt 10

wsicl 3.0

epsbext 1.0d-9

locmult on

locmomadd 2

pqmatdiag off

pqsingtol 1.0d-8

# PCG control options

lpcg off

lcfmmpcg on

lmxmompcg 20

pcgtol 1.0d-9

pcgtyp sp

In this example the three-dimensional system is defined ($periodic 3). The parameters of the unit cell are defined by the $cell keyword, with lengths and angles specified in atomic units and degrees. All six parameters are required, regardless the system periodicity. In 2D and 1D systems the aperiodic dimensions need to be large enough to enclose all atoms specified in the coord data group. An uniform grid of 27 (3 ⋅ 3 ⋅ 3) k-points is used. The datagroup $riper contains the most important options along with standard values for periodic calculations. More detailed discussion for each keyword is presented in section 21.2.7. If any of the options is missing, the standard value is used. For molecular calculations locmult should be switched to off as well as the lpcg since preconditioned CG iterative solver is implemented only for the molecular systems.