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How to run the NCA program

The program can be compiled on linux PC by typing "make PLATFORM=PC RELEASE=1". The second option produces the optimized code.

A short help can always be obtained by executing the program and giving no arguments. Thus typing nca gives the following output
Sig = sig.inp # The name of the input Self-energies
Ac = Ac.inp # The name of the input bath function
cix = cix.dat # The name of the input file containing information about bands and their degeneracy
out = . # The name of the output directory
gloc = gloc.out # The name of the output Green's function
sig = sig.out # The name of the output Self-energy
Ed = -2 # Energy level
U = 4 # Coulomb repulsion
T = 0.2 # Temperature
Q = 1 # Default average Q in grand-canonical ansamble
alpha = 0.5 # The fraction of the new self energy to be used in the next iteration
max_diff = 1e-06 # Criterium to finish the procedure
max_steps = 300 # Criterium to finish the procedure
StartLambda = -1 # Where to start searching for the lambda0
EndLambda = 1 # Where to stop searching for the lambda0
dLambda = 0.1 # Step in searching for the lambda
followPeak = -3 # Wheather to determin zero frequency from the diverging pseudo-particle
(-2: lamdba0==StartLambda, -1: Q==Q0, 0: follow b, 1: follow f, 2: foolow a)
prt = 1 # Weather to print intermediate results
MissDopSt = -100 # Missing doping due to projection and finite mesh starting at MissDopSt

All control parameters are printed with there default values. After the symbol # a short description of each parameter is also given. Below we will give some more description to each parameter but let us run an example program first.

The necessary files can be found in the subdirectory PC/work and PC/work/start. The example is for the f-electrons with around 6 electrons on the impurity. The crystal field splits the 7 band problem into 3+3+1 band problem (To generate the input file one thus needs to use 3 bands and degeneracy 6,6,2). All the impurity states with 4,5,6 and 7 electrons on the impurity are keept which results in a 64 nonequivalent pseudoparticle (atomic) states. The necessary coefficients $ F$'s to run the program are already prepared in the file PC/work/start/cix4567.cix.

To run the program, one also needs a bath spectral function (it is in PC/work/start/Ac.12) and starting guess for the pseudo self-energies (can be found in PC/work/start/Sigma.000). The input bath spectral function contain four columns, frequency and three nonequivalent bath spectral functions. The pseudo self-energy files contains 65 columns, in addition to frequency, a guess self-energy for all 64 pseudo particles.

An example of how to run the program can be found in the file history.nca in a subdirectory PC/work and reads

../nca Sig=start/Sigma.000 Ac=start/Ac.12 cix=start/cix4567.cix U=4 T=0.1 "Ed={-20.67,-20.58,-20.64}"

Each time the program is executed, the command line is saved (appended) to the file history.nca for easier restart of a job at a later time.

In the example, the self-consistency is reached after about 30 iterations (the difference between the steps below $ 10^{-6}$) and the following results are ready to be plotted

The spectral function obtained in this example is plotted in figure 1. At each iteration, the following information is written in the standard output
Figure 1: The spectral function in the example.
\includegraphics[width=0.50\linewidth angle=0]{spectra1.eps}

Finally, let me give some more details of every parameter of the program

Next: About this document ... Up: NCA_descrip Previous: How to generate the
Kristjan Haule 2004-08-23