PSI4 Installation

PSI4 is an open-source program for computational chemistry. In order for Qiskit’s chemistry module to interface PSI4, i.e. execute PSI4 to extract the electronic structure information necessary for the computation of the input to the quantum algorithm, PSI4 must be installed and discoverable on the system where Qiskit’s chemistry module is also installed.

Therefore, once PSI4 has been installed, the psi4 executable must be reachable via the system environment path. For example, on macOS, this can be achieved by adding the following section to the .bash_profile file in the user’s home directory:

# PSI4
alias enable_psi4='export PATH=/Users/username/psi4conda/bin:$PATH'

where username should be replaced with the user’s account name. In order for the chemistry module to discover PSI4 at run time, it is then necessary to execute the enable_psi4 command before launching Qiskit.