# adcc
`adcc` is a python-based framework to connect to arbitrary host
programs for running ADC calculations.

## Quick overview
Currently `adcc` supports all ADC(n) variants up to level 3,
that is:
- ADC(0)
- ADC(1)
- ADC(2)
- ADC(2)-x
- ADC(3)

For all of these, excluding ADC(3), the core-valence approximation
can be applied and for all variants one-particle
transition density matrices and excited states density matrices
are available. These can be used to compute properties such
as the oscillator strength in user code.
Both restricted as well as unrestricted references are supported.


## Installation
Once we have figured out how to do it, it should be as simple as
```
pip install adcc
```
Right now, the package is not
uploaded to [pypi](https://pypi.org), however.


## Developer setup
### Users with access to adccore source code
Having cloned this `adcc` repository,
proceed to clone `adccore` **into the `adcc` directory**,
that is, run
```
git clone https://path/to/adccore adccore
```
inside the directory, where this **README.md** file is found.
You should now have the following folder structure:
```
adcc/README.md
adcc/adcc/__init__.py
...
adcc/adccore/README.md
adcc/adccore/CMakeLists.txt
...
```
Afterwards build, test and (optionally) install `adcc`.
```
./setup.py test   # Builds and tests adcc
pip install .     # Installs adcc (optional)
```

### Users without access to adccore source code
Download the tarball of the compiled `adccore` library
into the `external/adccore` directory:
```
cd ./external/adccore
wget " https://path/to/binary/adccore-VERSION.tar.gz"
tar xzf adccore.tar.gz
cd ../..
```

Afterwards proceed as above, that is:
```
./setup.py test   # Builds and tests adcc
pip install .     # Installs adcc (optional)
```

## Commands of the `setup.py` script worth knowing
The following commands of the `setup.py` script are very useful
for development and worth knowing:

- `setup.py build_ext`: Build the `C++` part of `adcc` in the current directory.
  This includes `adccore` in case you have the source code repository set up as
  described above.
- `setup.py test`: Run the `adcc` unit tests via `pytest`. Implies `build_ext`.


## `adcc` and `pyscf` example
The following example runs an SCF in `pyscf` and an ADC(3) calculation on top:
```python
from pyscf import gto, scf
import adcc

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

# Initialise ADC memory (512 MiB)
adcc.memory_pool.initialise(max_memory=512 * 1024 * 1024)

# Run an adc3 calculation:
state = adcc.adc3(scfres, n_singlets=3, n_triplets=3, conv_tol=1e-6)

# Print the resulting states
print(state[0].describe())
print()
print(state[1].describe())
```
More examples can be found in the `examples` folder.