7.3 How to Perform a Calculation

7.3.1 Prerequisites

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.

7.3.2 Creating the Input File

To run riper type

riper > riper.out &

7.3.3 Example

$periodic 3  
  18.5911 16.5747 16.5747 90. 90. 90.  
  nkpoints 3 3 3  
  # 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.