title "Water TD-PBE0 resonant excitation" echo scratch_dir ./scratch permanent_dir ./perm start water ## ## aug-cc-pvtz / pbe0 optimized ## ## Note: you are required to explicitly name the geometry ## geometry "system" units angstroms nocenter noautoz noautosym O 0.00000000 -0.00001441 -0.34824012 H -0.00000000 0.76001092 -0.93285191 H 0.00000000 -0.75999650 -0.93290797 end ## Note: We need to explicitly set the "active" geometry even though there is only one geom. set geometry "system" ## All DFT and basis parameters are inherited by the RT-TDDFT code basis * library 6-31G end dft xc pbe0 end ## Compute ground state of the system task dft energy ## ## We excite the system with a quasi-monochromatic ## (Gaussian-enveloped) z-polarized E-field tuned to a transition at ## 10.25 eV. The envelope takes the form: ## ## G(t) = exp(-(t-t0)^ / 2s^2) ## ## The target excitation has an energy (frequency) of w = 0.3768 au ## and thus an oscillation period of T = 2 pi / w = 16.68 au ## ## Since we are doing a Gaussian envelope in time, we will get a ## Gaussian envelope in frequency (Gaussians are eigenfunctions of a ## Fourier transform), with width equal to the inverse of the width in ## time. Say, we want a Gaussian in frequency with FWHM = 1 eV ## (recall FWHM = 2 sqrt (2ln2) s_freq) we want an s_freq = 0.42 eV = ## 0.0154 au, thus in time we need s_time = 1 / s_time = 64.8 au. ## ## Now we want the envelope to be effectively zero at t=0, say 1e-8 ## (otherwise we get "windowing" effects). Reordering G(t): ## ## t0 = t - sqrt(-2 s^2 ln G(t)) ## ## That means our Gaussian needs to be centered at t0 = 393.3 au. ## ## The total simulation time will be 1000 au to leave lots of time to ## see oscillations after the field has passed. ## rt_tddft tmax 1000.0 dt 0.2 field "driver" type gaussian polarization z frequency 0.3768 # = 10.25 eV center 393.3 width 64.8 max 0.0001 end excite "system" with "driver" end task dft rt_tddft