Saddle
One and two-sided saddle point search methods
are implemented in FLAME. Note that not all
parameters apply to
all available saddle point search methods
when task is set to saddle.
saddle parameters
general saddle parameters
method: (string) Method for the saddle point search.
bar_saddle parameters
dbar: (real) The length of the bar/dimer in the bar-saddle method. In units of Bohr in configurational space.
default:
1.d-1
nstep: (integer) Maximal number of steps for the saddle search.
default:
1000
stepsize: (real) The initial step size for the saddle point search iterations. Will be adjusted based on a a feedback mechanism. Arbitratry units.
default:
20.d0
bar_contract: (logical) Activates the contraction of the bar size during the optimization. The final bar size can be set with dbar_contracted. The contraction occurs gradually over nstep_contract iterations.
default:
True
dbar_contracted: (real) The final bar size after contraction. In units of Bohr in configurational space.
default:
1.d-3
nstep_contract: (integer) Number of iterations to contract the bar from the initial value dbar to the final length dbar_contracted.
default:
40
fnrmtol_coarse: (real) The force norm tolerance that has to be reached to commence the contraction of the bar. Units in Ha/Bohr.
default:
1.d-2
fnrmtol_contracted: (real) The force norm tolerance for the convergence of the final, contracted bar. Units in Ha/Bohr.
default:
5.d-4
dimer parameters
list_random_displace: (list of integers) List of atomic indices that are displaced randomly before initiating the saddle optimization in the dimer method.
default:
No default value.
ampl: (real) The amplitude of the random displacement applied to the atoms listed by the key list_random_displace. In units of Bohr in configurational space.
default:
No default value.
dimsep: (real) The dimer separation in the dimer method. No default value given, must be set when the dimer method is invoked. In units of Bohr in configurational space.
default:
No default value.
splined_saddle parameters
np_splsad: (integer) Number of anchor points.
np_splsad-1 is the number of moving anchor points in the splined saddle method.
Note: with the default value of 2, the splined saddle will only have one moving achor point.
default:
2
np_neb: (integer) Number of NEB images.
np_neb-1 is the number of moving images in the nudged elastic band (NEB) method.
Note: with the default value of 2, the NEB will run with only one moving image.
default:
2
ns2: (integer) Number of extra points added to the number of anchor points in order to assist the maximization process, the inner loop of the splined saddle method.
default:
0
vdtol: (real) The convergence criterion in the maximization process in the inner loop of the splined saddle method. Units in Ha.
default:
1.d-1
htol: (real) The smallest value of the normalized pathway parameter between two neighboring points in the maximization process of the splined saddle method. Arbitrary units.
default:
2.d-2
alphax: (real) The step size of the optimizer in the NEB and splined saddle methods. Arbitrary units.
default:
5.d-1
docineb: (string) Activates the climbing image NEB.
default:
nooptions:
no: NEB without climbing image
yes: NEB with climbing image
doneb: (string) Activates NEB calculations.
default:
No default value.options:
no: No NEB calcualtion is performed
yes: NEB calculation is performed
pickbestanchorpoints: (string) Activates an automated selection of favored anchor points.
This feature is not well tested and we recommend setting this parameter to no.
default:
No default value.options:
no: anchor points are distributed uniformly in the beginning of simulation
yes: anchor points are initially selected to favor higher energy points based on estimates obtained by an interpolation.
runstat: (string) Determines whether a new or a restart run is performed.
default:
newoptions:
new: New run, the NEB images or splined saddle anchor points are initialized at the beginning of the run.
restart: Restart run, the NEB images or splined saddle anchor points are read from a file. Restart runs have not yet been well tested, so we currently do not recommend using it.
typintpol: (string) The type of interpolation in the maximization process of the splined saddle method.
default:
cubicoptions:
cubic: Natural cubic splines.
quintic: A spline using fifth-order polynomials. Rather unstable except for simple pathways.
fcalls_max: (integer) The maximum number of calls to force evaluation.
default:
100
fmaxtol_splsad: (real) The convergence criterion for the saddle optimization in the splined saddle method. Units in Ha/Bohr.
default:
2.d-4
fmaxtol_neb: (real) The convergence criterion for the saddle optimization in the NEB method. Units in Ha/Bohr.
default:
2.d-2
opt_method: The optimization method used in the saddle point search when using NEB or the splined saddle method.
default:
SDoptions:
SD: The steepest descent method.
BFGS: The Broyden–Fletcher–Goldfarb–Shanno (BFGS) method.