adapt - solver for differential equations which determine the full set of
discretization coefficients in adaptive logarithmic discretization approach
in numerical renormalization group

nrgchain - tridiagonalisation code for determining the tight-bidning
coefficients of the Wilson chain for NRG calculations

Copyright (C) 2008, 2009 Rok Zitko


adapt solves the differential equations which determine logarithmic
discretization coefficients in the form

  epsilon(x) = g(x) Lambda^(2-x),
  Epsilon(x) = f(x) Lambda^(2-x),
  
where epsilon(x) are the discretization mesh points and Epsilon(x) the
representative energies, while x=j+z is the mesh parameter which combines
the discretization interval number j=1,2,3,.. and the twist parameter z in
the interval [0:1]. For more details see

  Rok Zitko: "Adaptive logarithmic discretization for numerical
  renormalization group methods", Computer Physics Communications (2009).

and
 
  Rok Zitko, Thomas Pruschke: "Energy resolution and discretization
  artefacts in the numerical renormalization group", 
  Physical Review B 79, 085106 (2009).
  

nrgchain determines the coefficients xi (hopping constants) and zeta
(on-site energies) for a Wilson chain. It takes the output from adapt
as its input.


1. Installation

Modify "Makefile" if necessary, compile using "make" and copy the resulting
executables (adapt, nrgchain) to an appropriate location.

The discretization equation solver is written in pure ISO C++ without making
use of any external libraries, therefore it should be highly porable. The
tridiagonalization code makes use of the GNU MP Bignum library (multiple
precision), see http://gmplib.org/. (Tested with GMP version 3.0.5.)


2a. Usage (adapt)

Usage: adapt [P|N] [parameter_file]

Optional argument P or N specifies whether positive or negative frequency
part of the density of states is being discretized [default is "P"].

Argument parameter_file specifies which file contains parameters [default is
"param"].

Consult the sample parameter file for description of the parameters.


2b. Usage (nrgchain)

Usage: nrgchain [parameter_file]

Consult the sample parameter file for description of the parameters.


3. License

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.
	   
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
		       
  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA

The full text of the GPL General Public License can be found
in file LICENSE.


4. Contact information

"adapt" home-page: http://nrgljubljana.ijs.si/adapt/

Rok Zitko
"Jozef Stefan" Institute
F5 - Condensed matter physics
Jamova 39
SI-1000 Ljubljana
Slovenia

rok.zitko@ijs.si


5. Acknowledgements

'adapt' solver was developed during author's stay at the Institute for
theoretical physics, University of Goettingen, Germany. Fruitful discussions
with prof. Thomas Pruschke, computer support by GWDG, and support by the
German Science Foundation through SFB 602 are acknowledged.