# Get started

The quickest way to use MLatom is to run it {doc}`online <cloud>` on the
[Aitomistic Hub](https://aitomistic.xyz) or
[Aitomistic Lab@XMU](https://atom.xmu.edu.cn) — nothing to install. To run
locally, just install MLatom — it pulls in the required dependencies
automatically (including the PyTorch/TorchANI and geometry-optimization backends
the **AIQM2** example below uses). AIQM2 additionally needs the DFT-D4 program
(via conda):

```bash
pip install -U mlatom
conda install -c conda-forge dftd4
export dftd4bin=$(which dftd4)   # point MLatom at the dftd4 executable
```

See the {doc}`installation guide <installation>` for the full dependency list
and other methods.

## Quick start

Optimize the geometry of a water molecule with **AIQM2** — an AI-enhanced
quantum-mechanical method (native to MLatom, CHNO elements) that reaches
beyond-DFT accuracy at semi-empirical cost.

### Python API

```python
import mlatom as ml

mol = ml.data.molecule.from_xyz_string('''3

O    0.00000    0.00000    0.11779
H    0.00000    0.75545   -0.47116
H    0.00000   -0.75545   -0.47116
''')
aiqm2 = ml.methods(method='AIQM2')
opt = ml.optimize_geometry(model=aiqm2, initial_molecule=mol).optimized_molecule
print(opt.energy)          # optimized energy in hartree
```

To check your setup worked, the printed energy should be approximately:

```text
-76.3838
```

### Command line (input file)

The same calculation from the command line. Save the geometry as `init.xyz`:

```text
3

O    0.00000    0.00000    0.11779
H    0.00000    0.75545   -0.47116
H    0.00000   -0.75545   -0.47116
```

and the input as `geomopt.inp`:

```text
AIQM2               # method
geomopt             # task: geometry optimization
xyzfile=init.xyz    # input geometry
optxyz=opt.xyz      # output geometry
```

then run:

```bash
mlatom geomopt.inp
```

The optimized geometry is written to `opt.xyz`, and the output reports the
optimized energy (≈ -76.3838 hartree). You can also
{download}`download geomopt.inp <files/get_started/geomopt.inp>` and
{download}`init.xyz <files/get_started/init.xyz>`.

:::{note}
Prefer zero setup? Run these online on the
[Aitomistic Hub](https://aitomistic.xyz) or
[Aitomistic Lab@XMU](https://atom.xmu.edu.cn) (both powered by
[Protomia](https://aitomistic.com/protomia)) — no installation needed.
:::