Let's import the psi4 and forte modules, including the forte.utils submodule
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import psi4
import forte
import forte.utils
We will start by generating SCF orbitals for methane via psi4 using the forte.util.psi4_scf function
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xyz = """
0 1
C -1.9565506735 0.4146729724 0.0000000000
H -0.8865506735 0.4146729724 0.0000000000
H -2.3132134555 1.1088535618 -0.7319870007
H -2.3132183114 0.7015020975 0.9671697106
H -2.3132196063 -0.5663349614 -0.2351822830
symmetry c1"""
E_scf, wfn = forte.utils.psi4_scf(xyz, 'sto-3g', 'rhf', functional = 'hf')
Next we start forte, setup the MOSpaceInfo object specifying the number of orbitals, and start the integral object
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from forte import forte_options
forte.startup()
options = forte.forte_options
mos_spaces = {'RESTRICTED_DOCC' : [5], 'ACTIVE' : [0]}
mo_space_info = forte.make_mo_space_info_from_map(wfn,mos_spaces,[])
scf_info = forte.SCFInfo(wfn)
ints = forte.make_forte_integrals(wfn, options, mo_space_info)
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localizer = forte.Localize(forte.forte_options, ints, mo_space_info)
Once the Localize object is created, we specify which we want to be localized and can compute the unitary transformation
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localizer.set_orbital_space(['RESTRICTED_DOCC'])
localizer.compute_transformation()
From the localizer we can then extract the unitary transformation matrix that correspond to the orbital localizaition. Here we get the alpha part
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Ua = localizer.get_Ua()
We are now ready to read the MOs from psi4 and transform them by computing the product $\mathbf{C}' = \mathbf{C} \mathbf{U}$. We then place the orbitals back into psi4 by calling the copy function on wfn.Ca(). We have to do this because this function returns a smart pointer to the matrix that holds $\mathbf{C}$. If we assigned Ca_local via wfn.Ca() = Ca_local we would not change the orbitals in psi4.
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Ca = wfn.Ca()
Ca_local = psi4.core.doublet(Ca,Ua,False,False)
wfn.Ca().copy(Ca_local)
Lastly we generate cube files for all the occupied orbitals and visualize them. The resulting orbitals consist of a core orbital (which cannot be seen) and four localized C-H $\sigma$ bond orbitals
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cubes = forte.utils.psi4_cubeprop(wfn,path='cubes',nocc=5,nvir=0, load=True)
plot = forte.utils.cube_viewer(cubes)
plot
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forte.cleanup()