You’re getting the same fundamental error in both the interactive and batch version, though.
The ‘reinit: Reading from standard input’ line seemed off, since you were providing an argument for the input file. But all the references I find to running Siesta in their manual (section 3 and section 16) show something more like:
mpirun -np 4 /share/apps/chem/siesta-4.0.2/spar/siesta < dimer1prime.fdf > dimer1prime.out
and those examples line up with the idea that Siesta reads its commands from standard input, not by literally opening an input file specified as a command-line argument.
If the version of the command using < and > works correctly, then it’s definitely not a Slurm issue, it’s an issue with how you invoked Siesta.