Tutorial: orbitals and density with convergence checks
Inspect orbitals and charges, then test density convergence. You need wavefunction records, not just coordinates. Copy the packaged examples first:
The commands below use water. You can also try
./openwfn-examples/everyday-qc/ethanol.molden or
./openwfn-examples/everyday-qc/biphenyl.molden. Choose grid settings for each
molecule rather than assuming the water settings will converge.
1. Inspect and analyze
openwfn ./openwfn-examples/water.fchk doctor
openwfn ./openwfn-examples/water.fchk orbitals frontier
openwfn ./openwfn-examples/water.fchk population mulliken
openwfn ./openwfn-examples/water.fchk population lowdin
Record the spin channel, orbital indices, energies, and gap. The orbital-energy gap is not automatically an excitation energy. Differences between population schemes are expected because atomic charges are model-dependent partitions.
2. Converge total density
openwfn ./openwfn-examples/water.fchk density integrate \
--kind total --spacing 0.20 --padding 6.0
openwfn ./openwfn-examples/water.fchk density integrate \
--kind total --spacing 0.15 --padding 6.0
openwfn ./openwfn-examples/water.fchk density integrate \
--kind total --spacing 0.15 --padding 7.0
The integral should approach the molecular electron count. Choose settings based on convergence of the digits needed for the scientific conclusion; defaults are not universally sufficient.
3. Export a cube
openwfn ./openwfn-examples/water.fchk density cube water-density.cube \
--kind total --spacing 0.15 --padding 6.0
Cube files can be large and disclose coordinates and volumetric results. Record their controls and protect them as research data.
Read Orbitals and density and Validation status before interpreting results.