# QuAcK: a software for emerging quantum electronic structure methods

**Contributors:**
- [Pierre-Francois Loos](https://pfloos.github.io/WEB_LOOS)
- [Enzo Monino](https://enzomonino.github.io)
- [Antoine Marie](https://antoine-marie.github.io)
- [Anthony Scemama](https://scemama.github.io)
  
# What is it?

QuAcK is a small electronic structure program written in `Fortran 90` and developed at the Laboratoire de Chimie et Physique Quantiques [LCPQ](https://www.lcpq.ups-tlse.fr) (Toulouse, France).
QuAcK is usually used for prototyping purposes and the successful ideas are usually implemented more efficiently in [quantum package](https://quantumpackage.github.io/qp2/). QuAcK is an excellent place to start for experienced PhD students or postdocs as the code is simple and written in a fairly well-known and straightforward language. For beginners, we suggest having a look at [qcmath](https://github.com/LCPQ/qcmath/), a [Mathematica](https://www.wolfram.com/mathematica/)-based program to help newcomers in quantum chemistry easily develop their ideas. 

# Installation guide
The QuAcK software can be downloaded on GitHub as a Git repository
```
git clone https://github.com/pfloos/QuAcK.git
```

Then, one must define the variable `QUACK_ROOT`. For example, 
```
export QUACK_ROOT=$HOME/Work/QuAcK
```
You must also install [PySCF](https://pyscf.org) (for example using `pip`)
```
pip install pyscf
```

PySCF is used for the computation of one- and two-electron integrals (mainly).

# Quick start

```
QuAcK 💩 % cd $QUACK_ROOT
QuAcK 💩 % python PyDuck.py -h
usage: PyDuck.py [-h] -b BASIS [--bohr] [-c CHARGE] [--cartesian] [-fc FROZEN_CORE] [-m MULTIPLICITY] [--working_dir WORKING_DIR] -x XYZ

This script is the main script of QuAcK, it is used to run the calculation. If $QUACK_ROOT is not set, $QUACK_ROOT is replaces by the current
directory.

options:
  -h, --help            show this help message and exit
  -b BASIS, --basis BASIS
                        Name of the file containing the basis set in the $QUACK_ROOT/basis/ directory
  --bohr                By default QuAcK assumes that the xyz files are in Angstrom. Add this argument if your xyz file is in Bohr.
  -c CHARGE, --charge CHARGE
                        Total charge of the molecule. Specify negative charges with "m" instead of the minus sign, for example m1 instead of -1.
                        Default is 0
  --cartesian           Add this option if you want to use cartesian basis functions.
  -fc FROZEN_CORE, --frozen_core FROZEN_CORE
                        Freeze core MOs. Default is false
  -m MULTIPLICITY, --multiplicity MULTIPLICITY
                        Number of unpaired electrons 2S. Default is 0 therefore singlet
  --working_dir WORKING_DIR
                        Set a working directory to run the calculation.
  -x XYZ, --xyz XYZ     Name of the file containing the nuclear coordinates in xyz format in the $QUACK_ROOT/mol/ directory without the .xyz
                        extension
```

The two most important files are:
- the file `$QUACK_ROOT/input/methods` that gathers the methods you want to use.
- the file `$QUACK_ROOT/input/options` that gathers the different options associated these methods.

These files look like this
```
QuAcK 💩 % cat input/methods 
# RHF UHF KS MOM 
  T   F   F  F   
# MP2* MP3 
  F   F   
# CCD pCCD DCD CCSD CCSD(T) 
  F   F    F   F    F
# drCCD rCCD crCCD lCCD
  F     F    F     F
# CIS* CIS(D) CID CISD FCI
  F    F      F   F    F
# RPA* RPAx* crRPA ppRPA 
  F    F     F      F
# G0F2* evGF2* qsGF2* G0F3 evGF3
  F     F      F      F    F
# G0W0* evGW* qsGW* SRG-qsGW ufG0W0 ufGW
  T     F     F     F        F      F
# G0T0pp evGTpp qsGTpp G0T0eh evGTeh qsGTeh
  F      F      F      F      F      F
# * unrestricted version available
```
and
```
QuAcK 💩 % cat input/options 
# HF: maxSCF thresh   DIIS n_diis guess_type ortho_type mix_guess level_shift stability
      512    0.0000001  T    5     1          1          F         0.0         F
# MP: reg
      F
# CC: maxSCF thresh   DIIS n_diis
      64     0.0000001  T    5
# spin: TDA singlet triplet spin_conserved spin_flip 
        F   T       F       T              T 
# GF: maxSCF thresh  DIIS n_diis lin eta renorm reg
      256    0.00001 T    5      T   0.0 0      F
# GW: maxSCF thresh  DIIS n_diis lin eta COHSEX TDA_W reg
      256     0.00001  T  5      T    0.0  F    F     F 
# GT: maxSCF thresh  DIIS n_diis lin eta TDA_T reg
      256    0.00001  T    5      T   0.1 F     F  
# ACFDT: AC Kx  XBS
         F  T   T
# BSE: BSE dBSE dTDA evDyn ppBSE BSE2
        T    T    T    F   F     F
```

For example, if you want to run a calculation on water using the cc-pvdz basis set:
```
QuAcK 💩 % python PyDuck.py -x water -b cc-pvdz
```

<img src="https://lcpq.github.io/PTEROSOR/img/ERC.png" width="200" />

QuAcK is supported by the [PTEROSOR](https://lcpq.github.io/PTEROSOR/) project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 863481).