CASTEP file formats - TDDFT

The .tddft file contains detailed information about the results of a CASTEP calculation of excitations in the time-dependent DFT approach.

The header contains information about the structure, this block is followed by the representation of excited states as a superposition of Kohn-Sham one-electron bands. The overlap between occupied and unoccupied states gives a useful indication of the degree of charge transfer in every given excitation (if the value is significantly lower than 1.0, the TD-DFT description might be inaccurate since it does not take charge transfer into account).

The final section contains spectroscopic data; excitations energy, singlet or triplet character, level of convergence, and transition dipoles (the position operator between the ground-state wavefunction and the first order response wavefunction for the Nth excited state from TDDFT, ). The transition dipole is projected onto the Cartesian axes. The character can be marked as "spurious" to reflect the fact that there are mathematically valid solutions to the linear-response TDDFT eigenvalue problem that are not physical (Heßelmann and Görling, 2009). These are solutions that provide a pure Kohn-Sham orbital transition, with no contribution from the exchange-correlation action. In terms of observables, the matrix elements will be zero (numerically so for computed quantities), and therefore harmless unless you want to select a specific state, for example for a structure optimization.

The file has the following format:

BEGIN header
 CASTEP generated TDDFT output
 Highest occupied band for spin channel 1          4
 Highest occupied band for spin channel 2          4
 Energies in eV
 Unit cell vectors (A)
    2.087121    0.737909    1.278096
    0.000000    2.213726    1.278096
    0.000000    0.000000    2.556191
 Fractional Co-ordinates
 B         1     0.375000    0.375000    0.375000
 N         2     0.625000    0.625000    0.625000
END header
BEGIN Characterisation of states as Kohn-Sham bands
 State      Occ.         Unocc.        Overlap
	 1         3 -->          6       0.497606
	 1         3 -->          7       0.002308
	 1         4 -->          6       0.002307
	 1         4 -->          7       0.497591
 Total overlap for state    1 = 0.996985
 	 2         2 -->          6       0.494925
 	 2         2 -->          7       0.003908
 	 2         3 -->          5       0.012166
	 2         4 -->          5       0.488863
 Total overlap for state    2 = 0.999931
	 3         2 -->          6       0.003907
	 3         2 -->          7       0.494894
	 3         3 -->          5       0.488844
	 3         4 -->          5       0.012162
 Total overlap for state    3 = 0.999930
	 4         2 -->          6       0.055707
	 4         2 -->          7       0.104554
	 4         3 -->          5       0.097408
	 4         3 -->          6       0.155035
	 4         3 -->          7       0.169678
	 4         3 -->          8       0.022879
	 4         4 -->          5       0.061031
	 4         4 -->          6       0.164557
	 4         4 -->          7       0.153354
	 4         4 -->          8       0.013906
 Total overlap for state    4 = 0.999524
	 5         2 -->          6       0.104116
	 5         2 -->          7       0.055983
	 5         3 -->          5       0.059369
	 5         3 -->          6       0.166594
	 5         3 -->          7       0.147638
	 5         3 -->          8       0.013905
	 5         4 -->          5       0.100521
	 5         4 -->          6       0.161928
	 5         4 -->          7       0.164886
	 5         4 -->          8       0.022856
 Total overlap for state    5 = 0.999524
	 6         2 -->          5       0.640383
	 6         2 -->          8       0.036762
	 6         3 -->          7       0.165081
	 6         4 -->          6       0.153948
	 6         4 -->          7       0.001227
 Total overlap for state    6 = 0.999524
	 7         2 -->          6       0.003469
	 7         2 -->          7       0.330419
	 7         3 -->          5       0.327180
	 7         3 -->          6       0.020226
	 7         3 -->          7       0.143415
	 7         4 -->          5       0.008318
	 7         4 -->          6       0.145530
	 7         4 -->          7       0.020683
 Total overlap for state    7 = 0.999601
	 8         2 -->          6       0.331049
	 8         2 -->          7       0.003453
	 8         3 -->          5       0.008344
	 8         3 -->          6       0.145310
	 8         3 -->          7       0.020424
	 8         4 -->          5       0.322143
	 8         4 -->          6       0.020828
	 8         4 -->          7       0.147693
 Total overlap for state    8 = 0.999601
END Characterisation of states as Kohn-Sham bands
BEGIN TDDFT Spectroscopic Data
 State   Excitation Energy         Characterisation   Converged  Transition Dipoles (x,y,z)
	 1   6.5473971594196110E+000       Singlet           Yes     ( -8.1795306121346112E-006 -3.4564089336344694E-005)   (  3.2509688966730899E-005  1.2934755562188371E-006)   ( -1.3437677409466886E-005 -5.6089948278215118E-006)
	 2   6.5477931895610837E+000       Singlet           Yes     ( -2.1968719137211573E-004  7.0339626864693305E-004)   (  1.0286546711327392E-003 -3.1454865615340270E-003)   ( -5.4208674766353590E-004  1.5415051960497653E-003)
	 3   6.5477959245622372E+000       Singlet           Yes     (  1.0381162436738922E-003  3.2752571451736268E-003)   ( -5.8452216595283879E-005  1.0536872954158838E-005)   ( -3.5243315201338721E-004 -1.5030041786209258E-003)
	 4   6.9682670362142609E+000       Singlet           Yes     ( -2.1810910146322535E+000 -1.9091179444076365E+000)   (  8.3433521231804542E-001 -1.7962216514560714E+000)   (  3.9339280289056361E-001  1.7828535226058095E+000)
	 5   6.9682671623558505E+000       Singlet           Yes     ( -1.5662744900840448E+000  1.7205383620428409E+000)   (  2.8924977420656792E+000  2.6681152573246208E-001)   ( -9.5229913947131817E-001 -9.4845221714943473E-001)
	 6   6.9687191455611650E+000       Singlet           Yes     (  9.1444369167153461E-001  1.0029634036985597E+000)   (  1.2850826696348030E+000  1.2827320593679135E+000)   (  2.1774767906530905E+000  2.4030870284027319E+000)
	 7   7.2396275937532941E+000       unknown           No      ( -3.7375143373481468E-003 -1.4199767934261615E-003)   (  4.0335791099632701E-005 -3.2195054031300407E-004)   (  1.5911270043209580E-003  8.2897222000213877E-004)
	 8   7.2396370165366069E+000       unknown           No      ( -3.5721672861921752E-004 -7.8153744071166042E-004)   (  7.7446002261710029E-005  3.8407175453285536E-003)   (  1.5684794513495109E-004 -1.9778246154052992E-003)
END TDDFT Spectroscopic Data
		
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