Performing a parallel relativistic calculation of molecular EFG tensor is a simple two-step process

respect --scf --inp=my-input-file --nt=4 --scratch=/path/to/scratch/directory
respect --efg --inp=my-input-file --nt=4 --scratch=/path/to/scratch/directory

The first call of respect with the argument --scf performs the self-consistent field (SCF) optimization of ground-state molecular orbitals, which is a necessary prerequisite for the following EFG calculation. The second call of respect with the argument --efg actually performs the molecular EFG simulation.

The other arguments mandatory to respect are

• --inp
  specifies a name of the input file;

• --nt
  specifies the number of physical cores required for parallel execution;

• --scratch
  specifies a path to the scratch directory.

Note that the EFG tensor is related to the Nuclear Electric Quadrupole Hyperfine Interaction tensor (Q-tensor). Q-tensor elements (in MHz) equal the EFG tensor elements (in a.u.) times 234.9647 times the nuclear quadrupole moment (NQM in barn units, 1 barn = \(10^{-28}m^{2}\) ) and divided by \(2I(2I-1)\), where \(I\) is the nuclear spin. The Nuclear Quadrupole Coupling Constant (NQCC) (in MHz) is the largest value of the principal values of the EFG (in a.u.) times 234.9647 times the nuclear quadrupole moment (in barn units).

The input file my-input-file.inp should contain the input block scf: with some SCF-specific keywords, and the input block efg: with some EFG-specific keywords. A comprehensive list of all keywords can be found for SCF here and for EFG-tensor here. A simple example of my-input-file.inp looks like

#SCF input block
#4c Dirac-Kohn-Sham DFT (PBE0) calculation of SeH2 molecule
scf:

   geometry:
        Se    0.000000000   -0.000008000   -0.077624000
        H     0.000000000    1.049076000    0.961901000
        H     0.000000000   -1.048465000    0.962534000

   method: mdks/pbe0

   basis:
         H:  upc-1
         Se: ucc-pvdz

   charge:        0
   multiplicity:  1
   maxiterations: 30
   convergence:   1.0e-7
   nc-model:      gauss   #nuclear charge model


#EFG input block 
efg:
    active-atoms: Se    #eval. EFG tensor for the Se atom

As a final note, there are several important and worth-to-remember aspects associated with the input syntax, namely

• the input is case-insensitive
  This means that the program does not distinguish between uppercase and lowercase letters.

• the input is insensitive to the number of blank lines and/or comment lines
  All comments begin with the number sign (#), can start anywhere on a line and continue until the end of the line.

• the input is compliant with the dictionary syntax of the YAML markup language
  This means that each input line is represented either by a single block: statement or by a simple keyword:value pair, such as

block1:
    keyword1: value1 
    keyword2: value2  
    ...
    block2: 
      keyword3: value3
      keyword4: value4
      ...
    block3: 
           keyword5: value5
           keyword6: value6
           ...

It is essential to remember that all members of one block: are lines beginning at the same indentation level. Whitespace indentation is used to denote the block structure; however, tab characters are never allowed as indentation. The only exception to the YAML-based input syntax is the block geometry: which utilizes a simple xyz format for the molecular geometry specification.

Q: Is there a way to launch SCF and EFG calculations without the need to explicitly setup the scratch path by "--scratch=/path/to/scratch/directory"?

Yes, the argument "--scratch=/path/to/scratch/directory" can be saved to the file .respectrc in your home directory. If both the file and the command line argument exist, then ReSpect takes the scratch directory setting from the command line.