3.1 Running examples

As a final check that compilation was successful, you may want to run some or all of the examples (presently only one). To run the examples, you should follow this procedure:

1. Edit the environment_variables file in the main QUANTUM ESPRESSO directory, setting the following variables as needed:

   BIN_DIR: directory where executables reside
   PSEUDO_DIR: directory where pseudopotential files reside
   TMP_DIR: directory to be used as temporary storage area

The default values of BIN_DIR and PSEUDO_DIR should be fine, unless you have installed things in nonstandard places. The TMP_DIR variable must point to a directory where you have read and write permissions, with enough available space to host the temporary files produced by the example runs, and possibly offering good I/O performance (i.e., don't use an NFS-mounted directory). N.B. Use a dedicated directory, because the example script will automatically delete all data inside TMP_DIR. If you have compiled the parallel version of QUANTUM ESPRESSO (this is the default if parallel libraries are detected), you will usually have to specify a driver program (such as mpirun or mpiexec) and the number of processors: see Sec. for details. In order to do that, edit again the environment_variables file and set the PARA_PREFIX and PARA_POSTFIX variables as needed. Parallel executables will be started with a command line like this:

      $PARA_PREFIX neb.x $PARA_POSTFIX -inp file.in > file.out

For example, the command for IBM's POE looks like this:

      poe neb.x -procs 4 -inp file.in > file.out

therefore you will need to set PARA_PREFIX="poe", PARA_POSTFIX="-procs 4". Furthermore, if your machine does not support interactive use, you must run the commands specified below through the batch queuing system installed on that machine. Ask your system administrator for instructions.

Go to NEB/examples/examplex01 and execute:

      ./run_example

This will create a subdirectory results/ containing the input and output files generated by the calculation.

The reference/ subdirectory contains verified output files, that you can check your results against. They were generated on a Linux PC using the Intel compiler. On different architectures the precise numbers could be slightly different, in particular if different FFT dimensions are automatically selected. For this reason, a plain diff of your results against the reference data doesn't work, or at least, it requires human inspection of the results.