TDPW will read external electric field \(\mathbf{E}(t)\) from TDEFIELD.in file.
         According to Eq.(2,3,4), the vector potential \(\mathbf{k_A}\) ,which is the integral of electric field \(\mathbf{E}\), will be added in the Hamiltonian operator \(\mathcal{H_k}(\mathbf{G,G^{'}},t)\).
         If there is no TDEFIELD.in, the electric field \(\mathbf{E}(t)\) will be set to zero.
         There are nstep rows and 3 columns of values in TDEFIELD.in. The 3 values in line \(i\) is the electric field times \(10^5\), i.e. \(\mathbf{E_x}(t)\times 10^{5},\mathbf{E_y}(t)\times 10^{5},\mathbf{E_z}(t)\times 10^{5}\), at time \(t=i\times edt\).
         Now TDPW support length gauge by set GaugeField=F; tefield=T; emaxpos=0.96; eopreg=0.1. The meaning of tefield, emaxpos, eopreg=0.1 can refer to the manual of QE.

         For instance, TDEFIELD.in is like,

0.000373         0.000000        0.000000
0.000473         0.000000        0.000000
-0.000280        -0.000000       -0.000000
-0.002464        -0.000000       -0.000000
-0.004885        -0.000000       -0.000000
-0.002900        -0.000000       -0.000000
0.009653         0.000000        0.000000
0.031101         0.000000        0.000000
0.038987         0.000000        0.000000
-0.007789        -0.000000       -0.000000
-0.127871        -0.000000       -0.000000
-0.245284        -0.000000       -0.000000
...