Casida
Name CasidaCalcForces
Section Linear Response::Casida
Type logical
Default false
(Experimental) Enable calculation of excited-state forces. Requires previous vib_modes calculation.
Name CasidaCalcForcesKernel
Section Linear Response::Casida
Type logical
Default true
If false, the derivative of the kernel will not be included in the excited-state force calculation.
Name CasidaCalcForcesSCF
Section Linear Response::Casida
Type logical
Default false
If true, the ground-state forces will be included in the excited-state forces, so they are total forces.
If false, the excited-state forces that are produced are only the gradients of the excitation energy.
Name CasidaCalcTriplet
Section Linear Response::Casida
Type logical
Default false
For a non-spin-polarized ground state, singlet or triplet excitations can be calculated
using different matrix elements. Default is to calculate singlets. This variable has no
effect for a spin-polarized calculation.
Name CasidaDistributedMatrix
Section Linear Response::Casida
Type logical
Default false
Large matrices with more than a few thousand rows and columns usually do
not fit into the memory of one processor anymore. With this option, the
Casida matrix is distributed in block-cyclic fashion over all cores in the
ParOther group. The diagonalization is done in parallel using ScaLAPACK
or ELPA, if available. For very large matrices (>100000), only the
ParOther strategy should be used because the diagonalization dominates
the run time of the computation.
Name CasidaHermitianConjugate
Section Linear Response::Casida
Type logical
Default false
The Casida matrix is Hermitian, so it should not matter whether we calculate the upper or
lower diagonal. Numerical issues may cause small differences however. Use this variable to
calculate the Hermitian conjugate of the usual matrix, for testing.
Name CasidaKohnShamStates
Section Linear Response::Casida
Type string
Default all states
The calculation of the excitation spectrum of a system in the Casida frequency-domain
formulation of linear-response time-dependent density functional theory (TDDFT)
implies the use of a basis set of occupied/unoccupied Kohn-Sham orbitals. This
basis set should, in principle, include all pairs formed by all occupied states,
and an infinite number of unoccupied states. In practice, one has to truncate this
basis set, selecting a number of occupied and unoccupied states that will form the
pairs. These states are specified with this variable. If there are, say, 15 occupied
states, and one sets this variable to the value "10-18", this means that occupied
states from 10 to 15, and unoccupied states from 16 to 18 will be considered.
This variable is a string in list form, i.e. expressions such as "1,2-5,8-15" are
valid. You should include a non-zero number of unoccupied states and a non-zero number
of occupied states.
Name CasidaKSEnergyWindow
Section Linear Response::Casida
Type float
An alternative to CasidaKohnShamStates for specifying which occupied-unoccupied
transitions will be used: all those whose eigenvalue differences are less than this
number will be included. If a value less than 0 is supplied, this criterion will not be used.
Name CasidaMomentumTransfer
Section Linear Response::Casida
Type block
Default 0
Momentum-transfer vector for the calculation of the dynamic structure
factor. When this variable is set, the transition rates are determined
using an exponential operator instead of the normal dipole one.
Name CasidaParallelEigensolver
Section Linear Response::Casida
Type integer
Choose library to use for solving the parallel eigenproblem
of the Casida problem. This options is only relevant if a
distributed matrix is used (CasidaDistributedMatrix=true).
By default, elpa is chosen if available.
Options:
- casida_elpa:
Use ELPA library as parallel eigensolver
- casida_scalapack:
Use Scalapack as parallel eigensolver
Name CasidaPrintExcitations
Section Linear Response::Casida
Type string
Default write all
Specifies which excitations are written at the end of the calculation.
This variable is a string in list form, i.e. expressions such as "1,2-5,8-15" are
valid.
Name CasidaQuadratureOrder
Section Linear Response::Casida
Type integer
Default 5
Only applies if CasidaMomentumTransfer is nonzero.
Directionally averaged dynamic structure factor is calculated by
averaging over the results from a set of $\vec{q}$-vectors. The vectors
are generated using Gauss-Legendre quadrature scheme [see e.g.
K. Atkinson, J. Austral. Math. Soc. 23, 332 (1982)], and this
variable determines the order of the scheme.
Name CasidaTheoryLevel
Section Linear Response::Casida
Type flag
Default eps_diff + petersilka + lrtddft_casida
Choose which electron-hole matrix-based theory levels to use in calculating excitation energies.
More than one may be used to take advantage of the significant commonality between the calculations.
variational and lrttdft_casida are not usable with complex wavefunctions.
Note the restart data saved by each theory level is compatible with all the others.
Options:
- eps_diff:
Difference of eigenvalues, i.e. independent-particle approximation.
- petersilka:
The Petersilka approximation uses only elements of the Tamm-Dancoff matrix between degenerate
transitions (if no degeneracy, this is just the diagonal elements). Also called the "single-pole" approximation.
This is acceptable if there is little mixing between single-particle transitions.
Ref: M Petersilka, UJ Gossmann, and EKU Gross, Phys. Rev. Lett. 76, 1212 (1996);
T Grabo, M Petersilka,and EKU Gross, Theochem 501-502 353 (2000).
- tamm_dancoff:
The Tamm-Dancoff approximation uses only occupied-unoccupied transitions and not
unoccupied-occupied transitions.
Ref: S Hirata and M Head-Gordon, Chem. Phys. Lett. 314, 291 (1999).
- variational:
Second-order constrained variational theory CV(2)-DFT. Only applies to real wavefunctions.
Ref: T Ziegler, M Seth, M Krykunov, J Autschbach, and F Wang,
J. Chem. Phys. 130, 154102 (2009).
- lrtddft_casida:
The full Casida method. Only applies to real wavefunctions.
Ref: C Jamorski, ME Casida, and DR Salahub, J. Chem. Phys. 104, 5134 (1996)
and ME Casida, "Time-dependent density functional response theory for molecules,"
in Recent Advances in Density Functional Methods, edited by DE Chong, vol. 1
of Recent Advances in Computational Chemistry, pp. 155-192 (World Scientific,
Singapore, 1995).
Name CasidaTransitionDensities
Section Linear Response::Casida
Type string
Default write none
Specifies which transition densities are to be calculated and written down. The
transition density for the many-body state n will be written to a file called
rho_0n prefixed by the theory level. Format is set by OutputFormat.
This variable is a string in list form, i.e. expressions such as "1,2-5,8-15" are
valid.
Name CasidaWeightThreshold
Section Linear Response::Casida
Type float
Default -1.
Specifies the threshold value for which the individual excitations are printed.
i.e. juste-h pairs with weight larger than this threshold will be printed.
If a negative value (default) is set, all coefficients will be printed.
For many case, a 0.01 value is a valid option.
Name CasidaWriteDistributedMatrix
Section Linear Response::Casida
Type logical
Default false
Set to true to write out the full distributed Casida matrix to a file
using MPI-IO.
Name PhotonmodesFilename
Section Linear Response::Casida
Type string
Default “photonmodes”
Filename for photon modes in text format
- first line contains 2 integers: number of photon modes and number of columns
- each further line contains the given number of floats for one photon
mode