RTBSE : Change of input structure

More than one FT is carried out in the code, so the global FT parameters were moved to the &RTBSE section in the input. Also, allowed for more than one element of polarizability to be printed out.

docs/methods/properties/optical/rtbse.md

@@ -183,6 +183,16 @@ continue running the calculation in the same directory for longer time without r
 calculated time steps. Note that total length of the propagation time controls the energy/frequency
 precision, while timestep size controls the energy/frequency range.
 
+For applied field pulse not centered at zero in time, one can use
+[FT_START_TIME](#CP2K_INPUT.FORCE_EVAL.DFT.REAL_TIME_PROPAGATION.RTBSE.FT_START_TIME) to set the
+center of Fourier transforms to a provided time $t_0$. Furthermore, the damping $\gamma$ in the
+Fourier transform is controlled by
+[FT_DAMPING](#CP2K_INPUT.FORCE_EVAL.DFT.REAL_TIME_PROPAGATION.RTBSE.FT_DAMPING) parameter.
+Explicilty, in such case, the Fourier transform of function $f(t)$ is
+
+$$ f(\omega) = \int dt e^{i (\omega + i \gamma) t } f(t + t_0)
+$$
+
 ### Example Input
 
 A typical input file which runs the RTBSE propagation will have the
@@ -206,8 +216,6 @@ one
         &END MOMENTS
         &MOMENTS_FT
             FILENAME MOMENTS-FT
-            DAMPING 0.1 ! Exponential damping
-            START_TIME ! Fourier transform offset
         &END MOMENTS_FT
         &FIELD
             FILENAME FIELD
@@ -215,6 +223,7 @@ one
         &POLARIZABILITY
             FILENAME POLARIZABILITY
             ELEMENT 1 1
+            ELEMENT 2 2 ! print two different elements of tensor
         &END POLARIZABILITY
     &END PRINT
 &END REAL_TIME_PROPAGATION