psi4 command not found

In this troubleshooting guide we learn how to fix psi4 command not found error message

Introduction

When you run more command in linux terminal / console, you get the following error message

psi4: command not found

or when using sudo you get the following error message

sudo: psi4: command not found

Solutions to psi4: command not found

How To Fix psi4: command not found in Ubuntu / Debian / Kali Linux / Raspbian

In Ubuntu psi4 is provided by psi4 package.

psi4 is:

PSI4 is an ab-initio quantum chemistry program. It is especially designed to accurately compute properties of small to medium molecules using highly correlated techniques. PSI4 is the parallelized successor of PSI3 and includes many state-of-the-art theoretical methods.

It can compute energies, gradients and hessians for the following methods:

  • Restricted Hartree-Fock (RHF)

It can compute energies and gradients for the following methods:

  • Restricted, unrestricted and general restricted open shell Hartree-Fock (RHF/ROHF)
  • Restricted, unrestricted and general restricted open shell Densitry-Functional Theory, including density-fitting (DF-DFT)
  • Density Cumulant Functional Theory (DCFT)
  • Density-fitted Moeller-Plesset perturbation theory (DF-MP2)
  • Density-fitted Orbital-Optimized MP2 theory (DF-OMP2)
  • (Orbital-Optimized) MP3 theory (OMP3/MP3)
  • Coupled-cluster singles doubles (CCSD)
  • Density-fitted coupled-cluster singles doubles (DF-CCSD) and with perturbative triples (DF-CCSD(T))
  • Second-order approximate coupled-cluster singles doubles (CC2)
  • Equation-of-motion coupled-cluster singles doubles (EOM-CCSD)

Additionally, it can compute energies for the following methods:

  • Spin-component scaled MP2 theory (SCS-MP2)
  • Fourth order Moeller-Plesset perturbation theory (MP4)
  • Density-fitted symmetry-adapted perturbation theory (DF-SAPT)
  • Density-fitted complete active space SCF (DF-CASSCF)
  • Configuration-interaction singles doubles (CISD)
  • Full configuration-interaction (FCI)
  • Closed-shell Density-fitted coupled-cluster singles doubles (DF-CCSD)
  • Closed-shell Density-fitted Coupled-cluster singles doubles with perturbative triples (DF-CCSD(T))
  • Second/third-order approximate coupled-cluster singles doubles (CC2/CC3)
  • Mukherjee Multireference coupled-cluster singles doubles theory (mk-MRCCSD)
  • Mukherjee Multireference coupled-cluster singles doubles with perturbative triples theory (mk-MRCCSD(T))
  • Second order algebraic-diagrammatic construction theory (ADC(2))
  • Quadratic configuration interaction singles doubles (QCISD)
  • Quadratic configuration interaction singles doubles with perturbative triples (QCISD(T))
  • Density Matrix Renormalization Group SCF (DMRG-SCF), CASPT2 (DMRG-CASPT2) and CI (DMRG-CI)

Further features include:

  • Flexible, modular and customizable input format via Python
  • Excited state calculations with the EOM-CC2/CC3, EOM-CCSD, ADC(2), MRCI and mk-MRCC methods
  • Utilization of molecular point-group symmetry to increase efficiency
  • Internal coordinate geometry optimizer
  • Harmonic frequencies calculations (via finite differences)
  • Potential surface scans
  • Counterpoise correction
  • One-electron properties like dipole/quadrupole moments, transition dipole moments, natural orbitals occupations or electrostatic potential
  • Composite methods like complete basis set extrapolation or G2/G3
  • Scalar-relativistic corrections via two-component approach (X2C)

To fix this problem, we can install more using the command below.

sudo apt-get -y install psi4

This command might take some time to finish depending on your machine internet connection.

You can also use apt command to install psi4.

sudo apt -y install psi4

Or if you have aptitude installed you can use the following command.

sudo aptitude install psi4

Summary

In this tutorial we learn how to fix psi4 command not found error in Ubuntu / Debian / Kali Linux or Raspbian distribution.