Often users wish to perform several calculations in sequence, where the later calculations rely on results obtained from the previous ones. For example, a geometry optimization at a low level of theory, followed by a vibrational analysis and then, perhaps, single-point energy at a higher level. Rather than having the user manually transfer the coordinates from the output of the optimization to the input file of a vibrational analysis or single point energy calculation, Q-Chem can transfer them directly from job to job.
To achieve this requires that:
The READ variable is entered into the molecular coordinate input
$molecule READ $end
In this example, the job1 scratch files are saved in a directory $QCSCRATCH/job1 and are then made available to the job2 calculation. This is achieved with the following commands:
localhost-1> qchem job1.in job1.out job1 localhost-2> qchem job2.in job2.out job1
In this example, the job1 scratch files are saved in a directory $QCSCRATCH/job1 and are then made available to the job2 calculation.
Note: The program must be instructed to read specific scratch files by the input of job2.
The READ function can also be used to read molecular coordinates from a second input file. The format for the coordinates in the second file follows that for standard Q-Chem input, and must be delimited with the $molecule and $end keywords.
$molecule READ filename $end