ASE Manual Release 3.6.1.2825 CAMd - CampOS Wiki

ASE Manual, Release 3.6.1.2828
keyword type default value description
kpts list [1,1,1] Monkhorst-Pack k-point sampling
nbands int None Number of bands
meshcutoff float None Mesh cut-off energy in eV
basis str None Type of basis set (‘sz’, ‘dz’, ‘szp’, ‘dzp’)
xc str ’LDA’ Exchange-correlation functional.
pulay int 5 Number of old densities to use for Pulay mixing
mix float 0.1 Pulay mixing weight
width float None Fermi-distribution width in eV
charge float None Total charge of the system
label str ’siesta’ Name of the output file
A value of None means that SIESTA’s default value is used.
Extra FDF parameters
The SIESTA code reads the input parameters for any calculation from a .fdf file. This means that you can set
parameters by manually setting entries in this input .fdf file. This is done by the syntax:
>>> calc.set_fdf(’name_of_the_entry’, value)
For example, the EnergyShift can be set using
>>> calc.set_fdf(’PAO.EnergyShift’, 0.01 * Rydberg)
The complete list of the FDF entries can be found in the official SIESTA manual.
Customized basis-set
Standard basis sets can be set by the keyword basis directly in the Siesta calculator object. If a customized basis
is needed, it can be set as an FDF entry, as explained in the previous section.
As an example, we generate a triple-zeta triple-polarized (TZTP) basis for Au. Since the valence states are 6s and
5d, we will have 3 zeta orbitals for l=0 and 3 for l=2 plus 3 polarization orbitals for l=1. The basis can be defined
by
>>> value = ["""Au 2 split 0.00 #label, num. of l-shells,type,charge
>>> 0 3 P 3 #l,nzeta,’P’(opt):pol.functions,npolzeta
>>> 0.00 0.00 0.00 #rc of basis functions for each zeta function
>>> #0.00 => rc determined by PAO.EnergyShift
>>> 2 3 #l,nzeta
>>> 0.00 0.00 0.00"""] #rc
>>> calc.set_fdf(’PAO.Basis’,value=value)
The default basis set generation fails for Pt for some versions of Siesta. If this happens, you should specify the
basis set manually. This is exemplified below.
For Pt, using calc.set_fdf(’PAO.EnergyShift’, 0.1 * eV) is usually resonable, and a single-zeta
polarized basis set can be specified by writing:
# Define SZP basis set for Pt
calc.set_fdf(’PAO.Basis’,
["""\
Pt 2 # Species label, number of l-shells
n=6 0 1 P # n, l, Nzeta, Polarization, NzetaPol
0. # 0.0 => default [6.982 \n 1.000]
n=5 2 1 # n, l, zeta
0."""]) # 0.0 => default [5.172 \n 1.000]
A double-zeta polarized basis set for Pt may be specified by:
7.14. Calculators 115