# TDMomentumTransfer

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#### TDMomentumTransfer

Section Time-Dependent::Response
Type block

Momentum-transfer vector for the calculation of the dynamic structure factor. When this variable is set, a non-dipole field is applied, and an output file ftchd is created (it contains the Fourier transform of the charge density at each time). The type of the applied external field can be set by an optional last number. Possible options are qexp (default), qcos, qsin, or qcos+qsin. In the formulae below, $\vec{q}$ is the momentum-transfer vector.

Options:

• qexp:
External field is $e^{i \vec{q} \cdot \vec{r}}$.
• qcos:
External field is $\cos \left( i \vec{q} \cdot \vec{r} \right)$.
• qsin:
External field is $\sin \left( i \vec{q} \cdot \vec{r} \right)$.
• qbessel:
External field is $j_l \left( \vec{q} \cdot \vec{r} \right) Y_{lm} \left(\vec{r} \right)$. In this case, the block has to include two extra values (l and m).

Source information

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