When set to yes, states are stored in packed mode, which improves performance considerably. Not all parts of the code will profit from this, but should nevertheless work regardless of how the states are stored.
If GPUs are used and this variable is set to yes, Octopus will store the wave-functions in device (GPU) memory. If there is not enough memory to store all the wave-functions, execution will stop with an error.
See also the related HamiltonianApplyPacked variable.
The default is yes.