yambo Documentation

PWscf to yambo interface (p2y): direct approach

This approach is based on the QEXML library routines, kindly supplied by Andrea Ferretti from the WanT project, which act as a wrapper for the IOTK library routines of Giovanni Bussi, part of the standard Quantum-ESPRESSO distribution.

Step 1: Configuring p2y

Identify the version of PWscf you are using. Supported versions are: 3.1, 3.1.1, 3.2 (also for 3.2.x), and 4.0 or later.
Make sure you have access to the library $ESPRESSO/4.x/iotk/src/libiotk.a in your Quantum-ESPRESSO distribution. You may have to create it with make libiotk.
Configure p2y, specifying both the location of the iotk directory as well as the version of PWscf:
```
./configure --with-iotk='$ESPRESSO/4.0/iotk' --with-p2y=4.0'
```
Check that the links are found properly, and that p2y is configured for the right version of PWscf. You should see:
```
# [X] PW (4.0) support
```
Make the p2y executable (will appear in $yambo/bin):
```
make interfaces
```

Step 2: Create the [prefix].save directory files

Perform a self consistent run with PWscf (pw.x) in the usual manner.
Perform a non-self-consistent calculation with pw.x (nscf), making sure to
- include many unoccupied bands,
- collect the wavefunctions,
- converge well the unoccupied states,
- generate a set of k-points that spans the irreducible BZ (according to the symmetries)
For example:
```
 &control
    calculation = 'nscf'
    wf_collect= .true.  
 /
 &system
   nosym = .false.
   nbnd  = 200,
 /
 &electrons
    diago_thr_init = 1.0e-6
    diago_full_acc = .true.
 /
 K_POINTS {automatic}
 8 8 8 1 1 1
```
Check that the [prefix].save directory contains (nkpt) x K0000n directories, and that each of these contains an eigenvector file evc.dat

Step 3: Convert data to the yambo format with p2y.

Enter the [filename].save directory, and run p2y with the required options, e.g.
```
cd molecule.save
$yambo/bin/p2y -S -N
```
Note that it is safer to run p2y on a single processor.
Check the databases that are now in the SAVE directory. If you have linked to netCDF, you can inspect the files directly, e.g.:
```
ncdump SAVE/ns.db1 | less
```
and if fragmentation is being used (-S option), check that nkibz files of equal size, named ns.wf_fragments_n_1 (n=1...k), are created. See this page for a description of the yambo database format.
Otherwise you can ask yambo to report on the contents:
```
$yambo/bin/yambo -D -N
```
All ok? Well done: you are now ready to try the full yambo experience!

Still having problems? Try:

Tips and troubleshooting advice.