Mechanism for Generating Multiple Orbitals in SIESTA
Explore the split-valence method in SIESTA for generating multiple orbitals efficiently. Learn about controlling orbital range and the significance of PAO SplitNorm parameter in this comprehensive lecture by Javier Junquera.
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Presentation Transcript
Exercises on basis set generation Control of the range of the second- orbital: the split norm Javier Junquera
Default mechanism to generate multiple- in SIESTA: Split-valence method Starting from the function we want to suplement
Default mechanism to generate multiple- in SIESTA: Split-valence method The second- function reproduces the tail of the of the first- outside a radius rm
Default mechanism to generate multiple- in SIESTA: Split-valence method And continuous smoothly towards the origin as (two parameters: the second- and its first derivative continuous at rm
Default mechanism to generate multiple- in SIESTA: Split-valence method The same Hilbert space can be expanded if we use the difference, with the advantage that now the second- vanishes at rm (more efficient)
Default mechanism to generate multiple- in SIESTA: Split-valence method Finally, the second- is normalized rm controlled with PAO.SplitNorm
Meaning of the PAO.SplitNorm parameter PAO.SplitNorm is the amount of the norm (the full norm tail + parabolla norm) that the second- split off orbital has to carry (typical value 0.15)
Bulk Al, a metal that crystallizes in the fcc structure Go to the directory with the exercise on the energy-shift More information at the Siesta web page http://www.icmab.es/siesta and follow the link Documentations, Manual Inspect the input file, Al.energy-shift.fdf As starting point, we assume the theoretical lattice constant of bulk Al FCC lattice Sampling in k in the first Brillouin zone to achieve self-consistency
For each basis set, a relaxation of the unit cell is performed Variables to control the Conjugate Gradient minimization Two constraints in the minimization: - the position of the atom in the unit cell (fixed at the origin) the unit cell lattice vectors to 60 - the shear stresses are nullified to fix the angles between , typical of a fcc lattice
The splitnorm: Variables to control the range of the second- shells in the basis set
The splitnorm: Run SIESTA for different values of the PAO.SplitNorm Then, run SIESTA Edit the input file and set up PAO.SplitNorm 0.10 $siesta < Al.splitnorm.fdf > Al.splitnorm.0.10.out
For each splitnorm, search for the range of the orbitals Edit each output file and search for:
For each splitnorm, search for the range of the orbitals Edit each output file and search for: We are interested in this number
For each splitnorm, search for the range of the orbitals Edit each output file and search for: The lattice constant in this particular case would be 2.037521 2 = 4.075042
For each energy shift, search for the timer per SCF step We are interested in this number
The SplitNorm: Run SIESTA for different values of the PAO.SplitNorm Then, run SIESTA Edit the input file and set up PAO.SplitNorm 0.15 $siesta < Al.splitnorm.fdf > Al.splitnorm.0.15.out Try different values of the PAO.EnergyShift PAO.SplitNorm 0.10 $siesta < Al.splitnorm.fdf > Al.splitnorm.0.10.out PAO.SplitNorm PAO.SplitNorm 0.25 PAO.SplitNorm 0.20 $siesta < Al.splitnorm.fdf > Al.splitnorm.0.20.out $siesta < Al.splitnorm.fdf > Al.splitnorm.0.25.out $siesta < Al.splitnorm.fdf > Al.splitnorm.0.30.out 0.30
Analyzing the results Edit in a file (called, for instance, splitnorm.dat) the previous values as a function of the SplitNorm
Analyzing the results: range of the orbitals as a function of the split norm $ gnuplot $ gnuplot> plot splitnorm.dat" u 1:2 w l, splitnorm.dat" u 1:3 w l $ gnuplot> set terminal postscript color $ gnuplot> set output range-2zeta.ps $ gnuplot> replot The larger the SplitNorm, the smaller the orbitals
