The current revision of the comprehensive CNLS frequency-response fitting software, LEVM/LEVMW, V.8.13, is now available (May, 2015) at no cost. It includes both the LEVM program files for MS-DOS and new LEVMW files for full operation in WINDOWS. Some recent revisions are discussed on pp. 3-5 (ROE), and 4-9-10 and 5-16-19 (ordinary and anomalous diffusion models and generation-recombination effects) of the manual.
It is no longer necessary to get LEVM through Solartron, as in the past. You can now download the full program files, LEVMWL.zip, and the manual, LEVMMANUAL.pdf, from here by clicking on these items. See also: http://groups.google.com/group/impedance-spectroscopy for information on the newImpedance Spectroscopy study/help group.
Install the download to a temporary empty directory. The program files are provided in compressed form. It is particularly important to print the entire manual before beginning work with LEVM/LEVMW. The first six pages of the manual provide valuable information about LEVMW and how to start to use it immediately. If you experience a problem downloading the LEVM/LEVMW material, please send me an email message.
The full program material involves a total of about 6 MB of files or more, and the 170-page manual, which is essential. LEVMW runs directly on a PC under WINDOWS. Alternatively, LEVM requires either MS-DOS, or the MS-DOS mode of WINDOWS, and all its FORTRAN source code is included, along with an executable version, so the program may be compiled for any other machine or operating system.
In addition to providing a very powerful complex nonlinear least squares (CNLS) procedure for fitting small-signal frequency response data, LEVM/LEVMW also allows transient data to be fit to a model; it also includes provision for solving the inverse problem of estimating the distribution of the relaxation times function present from either type of data; and it can be used for data analysis and as a way of verifying that data satisfy the Kronig-Kramers transform relations, one superior to, and simpler than, direct KK integral transformation.
The LEVM program can be recompiled to use any fitting model which can be mathematically specified, for any number of data points (within the limitation of available memory). This is not usually necessary since the current version of the program allows fitting to many thousands of equivalent circuits which may involve more than 35 different distributed circuit elements. More description of an earlier version of LEVM appears in Solid State Ionics 23(1987)61. It has been very much improved and updated since then. The present LEVMW and LEVM versions 8.13 are much more general, versatile, and powerful than any other CNLS program that I know of and are a big improvement over earlier versions of LEVM.
If you get and use LEVMW/LEVM, I believe you will find it to be very helpful. I am still involved with the program, although Evgenij Barsoukov and Andry Gorkovenko will gradually take over support of it in coming years. For now, I would be interested in hearing of your experience with it. In particular, please notify me by email of any bugs you may discover of any problems you encounter in using it. Best of luck.
LEVM and LINUX:
Although the LEVM/LEVMW source files are available for recompiling in LINUX, a helpful correspondent has informed me that one can use the WINE emulator program, available free from www.winehq.org, to run LEVM using either a command-line or GUI approach (8/28/09).
SOME FEATURES OF CNLS PROGRAM LEVMW/LEVM
- Millions of built-in circuit possibilities available. New fitting models can be easily added since all source code is included.
- > 10 different weighting choices are available, and weighting parameters may be free parameters of the fit
- > about 37 different distributed circuit elements (DCE’s) available for circuits
- Complex-, real-, or imaginary-part fitting is possible
- A complex-fit optimization procedure is available
- Input data may be in Z, Y, E (complex epsilon), or M form
- Fitting or simulation may be at Z, Y, E, or M level
- Input/output may be in rectangular, polar, or log-polar form
- Applicable for conductive, dielectric, or mixed systems, including semiconductors, electrolytes, polymers, etc. Allows simultaneous fitting of data involving separate conductive-system and dielectric-system dispersions
- Fitting of transient-response data is possible for many response models
- Powerful 2- and 3-D plotting program included and a direct Windows graphics program
- Subtraction of the effects of selected circuit elements possible
- “Measurement-model” fitting and Kronig-Kramers testing available
- Estimation of distributions is possible by powerful methods of inversion of frequency or transient response data. This allows accurate transformation of wide-range data from time-to-frequency or vice versa without the need for Fourier transformation
- Several types of conductive-system dispersion models available for fitting
- Accurate stretched-exponential (KWW) fitting models included
- New generalized-exponential-distribution fitting model available
- Many of the fitting models may be used with or without adjustable small-tau cutoff of the distribution of relaxation times (tau) associated with the response, and the cutoff point may be a free parameter of the fit. This is superior to the Ngai Coupling method.