Restart files

Writing restart files

It is possible to save a ground state by writing a .gpw file. This saves the density, potential, eigenvalues and other information.

Use the write() method. For example calc.write('xyz.gpw').

• To also save the (potentially very large) wavefunctions, use calc.write('xyz.gpw', mode='all').

With “New GPAW” there are also two ways to produce smaller .gpw files:

• To avoid saving the (potentially large) PAW projections, use calc.write('xyz.gpw', include_projection=False).

• To further save space you can save the file in single-precision representation using calc.write('xyz.gpw', precision='single'). Note that reloading the file will load it as double-precision, so further processing will always be double precision.

Tip

You can register an automatic call to the write method, every n’th iteration of the SCF cycle like this:

calc.attach(calc.write, n, 'xyz.gpw')

or:

calc.attach(calc.write, n, 'xyz.gpw', mode='all')

This can be useful for very expensive calculations, where the SCF cycle may be interrupted before it completes. In this way, you can resume the calculation from an intermediate electronic structure.

Reading restart files

The calculation can be read from file like this:

calc = GPAW('xyz.gpw')

or this:

atoms, calc = restart('xyz.gpw')