# adcc: Seamlessly connect your program to ADC¶

Note

This documentation page is still under construction.

ADC-connect – or adcc in short – is a Python-based framework to connect to arbitrary programs and perform calculations based on the algebraic-diagrammatic construction approach (ADC) on top of their existing self-consistent field (SCF) procedures. Four SCF codes can be used with adcc out of the box, namely molsturm, psi4, PySCF, and veloxchem.

The range of supported algebraic-diagrammatic construction (ADC) methods includes the ADC(n) family up to level 3, including variants such as spin-flip and core-valence separation. For all methods transition and excited state properties are available. See the Performing calculations with adcc for more details. Recently we submitted a paper about adcc, see [HSF+20].

## Getting a first taste¶

You may interactively try adcc from your browser at https://try.adc-connect.org. Alternatively keep reading for a small code snippet, which shows how to perform an ADC(3) calculation for 3 singlet excited states of water on top of a restricted Hartree-Fock reference computed with PySCF.

```from matplotlib import pyplot as plt
from pyscf import gto, scf
import adcc

# Run SCF in pyscf
mol = gto.M(
atom='O 0 0 0;'
'H 0 0 1.795239827225189;'
'H 1.693194615993441 0 -0.599043184453037',
basis='cc-pvtz',
unit="Bohr"
)
scfres = scf.RHF(mol)
scfres.conv_tol = 1e-13
scfres.kernel()

# Run an ADC(3) calculation, solving for 3 singlets
state = adcc.adc3(scfres, n_singlets=3)

# Broaden the peaks and plot the resulting spectrum
state.plot_spectrum(broadening='lorentzian')
plt.show()
```

Sounds interesting? See Installation and Performing calculations with adcc for installation instructions and some more information to get going.