This example is adapted from cp2k/benchmarks/QS/H2O-64.inp.

First trial: energy calculation as simple as possible

Please follow the official tutorial to understand the sections/keywords used in input.inp, including:

GLOBAL: global setup (e.g., name, run type, etc.)
FORCE_EVAL/SUBSYS: system information (e.g., cell, atoms, etc.)

Instead of using COORD section (as in the website), atomic coordinates can also be written in an additional file (e.g., coord.xyz) and be included via
```
&TOPOLOGY
    COORD_FILE_FORMAT XYZ
    COORD_FILE_NAME coord.xyz
&END TOPOLOGY
```
FORCE_EVAL/DFT: DFT setup
- SCF: convergence, maximum number of SCF cycles, etc.
- XC: exchange-correlation functional
- BASIS_SET_FILE_NAME and POTENTIAL_FILE_NAME: Gaussian basis set and pseudopotential
- (optional) MGRID: multigrid settings -> how the basis set would be used for periodic systems

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