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Section Time-Dependent::TD Output
Type block

[WARNING: This is a very experimental feature] To be used with TDOutput = populations. The population of the excited states (as defined by <Phi_I|Phi(t)> where |Phi(t)> is the many-body time-dependent state at time t, and |Phi_I> is the excited state of interest) can be approximated – it is not clear how well – by substituting for those real many-body states the time-dependent Kohn-Sham determinant and some modification of the Kohn-Sham ground-state determinant (e.g., a simple HOMO-LUMO substitution, or the Casida ansatz for excited states in linear-response theory. If you set TDOutput to contain populations, you may ask for these approximated populations for a number of excited states, which will be described in the files specified in this block: each line should be the name of a file that contains one excited state.

This file structure is the one written by the casida run mode, in the files in the directory *_excitations. The file describes the "promotions" from occupied to unoccupied levels that change the initial Slater determinant structure specified in ground_state. These promotions are a set of electron-hole pairs. Each line in the file, after an optional header, has four columns:

i a $\sigma$ weight

where i should be an occupied state, a an unoccupied one, and $\sigma$ the spin of the corresponding orbital. This pair is then associated with a creation-annihilation pair $a^{\dagger}{a,\sigma} a{i,\sigma}$, so that the excited state will be a linear combination in the form:

$\left|{\rm ExcitedState}\right> = \sum weight(i,a,\sigma) a^{\dagger}{a,\sigma} a{i,\sigma} \left|{\rm GroundState}\right>$

where weight is the number in the fourth column. These weights should be normalized to one; otherwise the routine will normalize them, and write a warning.

Source information

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