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This module is automatically invoked by the Slapaf module.
This is the preferred mode of operation! In connection with numerical gradients
it will ensure that the rotational and translational invariance is fully
utilized in order to reduce the number of used displacements.
The Alaska module compute analytic or for numerical gradients requests the execution of
an alternative module.
The Alaska module figures out
the method automatically. Analytic methods are implemented for the HF, MBPT2, KS-DFT, and
RASSCF and SA-CASSCF method. Numerical methods are implemented for SCF, KS-DFT, RASSCF,
MBPT2, CCSDT, the CASPT2 and MS-CASPT2 methods, including the use of the Cholesky
decomposition for the methods were that has been implemented.
Both analytic and numerical procedures are parallelized.
For SA-CASSCF gradient the Alaska module will automatically
start up the MCLR module if required.
Gradients of the energy with respect to nuclear coordinates can be computed for
any type of wave function as long as an effective first order density matrix, an
effective Fock matrix, and an effective second order density matrix is provided.
The term effective is related to that
these matrices in the case of non-variational parameters in the wave function
(e.q. CI, MP2, CASPT2, etc.) are modified to include contributions from
the associated Lagrange
multipliers. The gradient expression apart from these modifications is
the same for any wave function type. ALASKA
is the gradient program, which will generate
the necessary integral derivatives and combine them with the matrices
mentioned in the text above.
ALASKA is written such that gradients can be
computed for any kind of basis function that SEWARD will accept.
ALASKA is able to compute the following integral derivatives:
- overlap integrals,
- kinetic energy integrals,
- nuclear attraction integrals (point charges or finite nuclei),
- electron repulsion integrals,
- external electric field integrals,
- ECP and PP integrals,
- reaction field integrals,
- and Pauli repulsion integrals.
two different integration schemes
to generate the
one- and two-electron integral derivatives.
The nuclear attraction and electron repulsion
integrals are evaluated by a modified Rys-Gauss quadrature .
All other integral
derivatives are evaluated with the Hermite-Gauss quadrature. The same
restriction of the basis sets applies as to SEWARD.
None of the integral derivatives are written to disk but rather combined
immediately with the corresponding matrix from the wave function.
At present the following limitations are built into ALASKA:
|Max number of unique basis functions:
|Max number of symmetry independent centers:
|Highest angular momentum:
|Highest symmetry point group:
The module is parallelized over the displacements, which in case of large jobs gives a linear
speed up compared to a serial execution, although in order to obtain this it is important to
choose the number of nodes such that the number of contributing perturbations is a multiple of
the number of nodes. For a given molecule the number of perturbations equals the number of atoms
times 6 (a perturbation with plus and minus delta for each of the three axes). Symmetry can of
course reduce this number.
ALASKA depends on the density and Fock matrices generated by
SCF or RASSCF. In addition it needs the basis set
specification defined in SEWARD.
The dependencies of the numerical part of the module is the union
of the dependencies of the SEWARD,
All these dependencies, however, are totally transparent to the user.
Apart from the standard input unit ALASKA
will use the following input
files: RYSRW, ABDATA, ONEINT, RUNFILE
(for more information see ).
The files of the SEWARD,
modules are needed for the numerical procedure.
In addition to the standard output unit ALASKA will generate the following
|RUNFILE||The runfile is updated with information needed by the SLAPAF
ALASKA will write the molecular Cartesian gradients on this file.
|ALASKA.INPUT||File with the latest input processed by ALASKA.
Below follows a description of the input to ALASKA.
Note that input options are related to the analytic gradient procedure if
not otherwise noted!
In addition to the keywords and the comment lines the input may contain blank
lines. The input is always preceded by the program name:
Optional keywords for analytical gradients
|TEST||With this keyword the program will process only the input.
It is a debugging aid to help you check your input.
|NAC||Requests a calculation of the nonadiabatic coupling vector between the
two specified roots in a SA-CASSCF calculation.
|NOCSF||In a NAC calculation, neglects the so-called CSF contribution.
Note that this contribution is responsible for the translational and
rotational non-invariance, and it has been suggested that not including
it may give more physical results in dynamics simulations .
|ONEOnly||Compute only the nuclear repulsion and one-electron integrals
contribution to the gradient. The default is to compute all
contributions to the molecular gradient.
|CUTOff||Threshold for ignoring contributions to the molecular gradient
follows on the next line. The default is 1.0d-7. The prescreening
is based on the 2nd order density matrix and the radial
overlap contribution to the integral derivatives.
|OFEMbedding||Performs a Orbital-Free Embedding gradient calculation, available only in combination with Cholesky or RI integral representation.
The runfile of the environment subsystem renamed AUXRFIL is required.
An example of input for the keyword OFEM is the following:
(see the OPTIONAL keyword :kword:`DFMD` below).
The keyword OFEM requires the specification of two functionals in the form fun1/fun2, where fun1 is the functional
used for the Kinetic Energy (available functionals: Thomas-Fermi, with acronym LDTF, and the NDSD functional), and where
fun2 is the xc-functional (LDA, LDA5, PBE and BLYP available at the moment).
|DFMD||In combination with OFEM, specifies the fraction of correlation potential to be added to the OFE potential (zero for
KSDFT and one for HF).
|POLD||The gradient is printed in the old format. Note: by default gradient
is not printed any longer.
|PNEW||The gradient is printed in the new human-readable format.
|VERBose||The output will be a bit more verbose.
|SHOW gradient contributions||The gradient contributions will be printed.
Optional keywords for numerical gradients
|NUMErical||Forces the use of numerical gradients even if analytical ones
are implemented. The default is to use analytical gradients whenever
|ROOT||Specifies which root to optimize the geometry for, if there is more than
one root to choose from. In a RASSCF optimization, the default is to
optimize for the same root as is relaxed. In a MS-CASPT2 calculation, the
default is to optimize for root 1. It can be used to override the default
root in an analytical calculation too.
|DELTa||For use with numerical gradients only!
The displacement for a given center is chosen as the distance to the nearest
neighbor, scaled by a factor. This factor can be set through the DELTa
keyword. The default value is 0.01.
|KEEPOldGradient||When computing numerical gradients with constraints, the gradient of the constrained degrees
of freedom is normally set to zero. If this keyword is specified, the existing value of the gradient
(probably computed analytically with a different method) is maintained instead.
This is used, in combination with NGEXclude in Gateway (or ``phantom''
constraints), to set up composite gradients .
The following is an example of an input which will work for
almost all practical cases. Note that it is very rarely that you need to run
this program explicitly. It is usually controlled by the program
Next: 8.2 averd
Up: 8. Programs
Previous: 8. Programs