University of MichiganAnn Arbor, MI 48109-2143

Climate and Space Sciences and Engineering

MultiWell Program Suite

J. R. Barker, T. L. Nguyen, J. F. Stanton, C. Aieta, M. Ceotto,
F. Gabas, T. J. D. Kumar, C. G. L. Li, L. L. Lohr, A. Maranzana,
N. F. Ortiz, J. M. Preses, J. M. Simmie, J. A. Sonk, and P. J. Stimac


This is the MultiWell web site. Contact John R. Barker at for further information or to be added to the email list.

Thermodynamics Database-2017.2: Update (May 2017)

Thanks to John Simmie, we have updated the Multiwell Thermodynamics Database by adding 17 additional chemical species. The new version is available on the Downloads page.

ktools v.2017ab: Update (March 2017)

Our new code, ktools, is a beta version and will be updated relatively frequently in response to users' reports of problems, etc. This updated version corrects some problems with formatting and with handling data files that are organized by users in unanticipated ways. None of the numerical results are affected. Please let us know about any problems you may encounter. We also welcome suggestions that will improve the code's usefulness. This new version is included in the (updated) multiwell-2017 Linux/unix packaeg; we do not yet offer a Windows version.

NEW IN VERSION 2017 (February 2017)

1. ktools (New Code): J-Resolved Microcanonical VTST: This new code (written mostly by Jason A. Sonk, who has joined the MultiWell Team) is an implementation of angular-momentum-resolved microcanonical variational transition state theory, which is suitable for barrierless reactions. Given information at points along the reaction path, the code automatically searches for transition states (TSs) at every E,J. If multiple TSs at the same E,J are found along the path, the code automatically uses W. H. Miller's unified statistical model to calculate their net effect. The output includes 2D (functions of E,J) rate constants and sums and densities of states. It also reports canonical (thermal) rate constants obtained by averaging over the thermal distribution. At the user's option, the 2D quantities are summed over J to obtain the 1D variables (functions of E), which are suitable for use in MULTIWELL and other 1D master equations. [This code is a beta-version: please tell us about any problems and bugs. The Windows version is not yet available, but we hope to post it soon.]

2. TS (New Code): J-resolved steady-state master equation solver: This new code (developed by Lam Nguyen and John Stanton) uses eigenvalue methods to solve the explicit 2D (i.e. depends on E,J) steady-state master equation, which was simplified by using the frozen-J approximation. This code should be particularly useful for chemical activation problems. Because of its structure, the code and TS User Manual are supplied in a separate directory and must be compiled separately from the rest of the MultiWell package. [This code should be regarded as a beta-version: please tell us about any problems and bugs.]

3. DENSUM, SCTST, and BDENS: enhancement: "TOP", the type of degree of freedom (DOF) for symmetric tops, has been added to these codes (it was already available in THERMO). This type of DOF is appropriate for the external rotations of a non-linear polyatomic. It is rigorously correct for a rigid symmetric top (e.g. it enforces the requirement that the K quantum number can only range from -J to +J) and is a good approximation for a non-symmetrical molecule that is treated as a quasi-symmetric top. This quasi-symmetric top approximation is obtained by replacing the two most-similar rotational constants for the non-symmetrical molecule with their geometric mean to obtain B2, the rotational constant corresponding to the 2-dimensional rotor in a true symmetric top; the remaining rotational constant (B1) is used with B2 in the equation for the rotational energy of a symmetric top (see the MultiWell User Manual).

4. THERMO: Enhancements: Several significant revisions have been made that improve convenience and reporting, but have no effect on numerical results.

(a) A new output file (thermo.details) reports heat capacity, entropy and enthalpy function for DOF at 298.15 K; the contributions from several groups of DOFs are reported at every temperature.

(b) The maximum length of chemical Names has been increased from 10 characters to 20 characters. (In future, this change will be made to other codes in the MultiWell Program Suite.)

(c) Previously, there were 3 comment lines for each chemical species. Now, up to 20 comment lines may be used (up to 150 characters, each). The first non-blank character in each comment line must be "!" (omit the quotation marks). This will require that older data files be revised slightly in order to run the new version.

(d) Previously, only certain upper/lower case combinations were recognized for key words and other character constants. Now, any combination of upper/lower case is recognized. (In future, this feature will be added to other codes in the MultiWell Program Suite.)

5. MULTIWELL THERMODYNAMICS DATABASE: Enhancements: Professor John M. Simmie (Galway) has joined the MultiWell team and is helping with the database. Many new species have been added to the database, including a number of Criegee intermediates and many species with parameters that are known only from quantum chemical calculations.

6. Hindered Rotor Codes: improvement: In previous versions of DENSUM, SCTST, BDENS, PARADENSUM, and THERMO, the hindered rotor states were extended to high energies by using the Pitzer Rotor approximation. It has been found that this measure is not only unnecessary, but it poorly represents the eigenvalues for some unsymmetrical hindered rotors at intermediate energies. Because the hindered rotor eigenstates are now reported explicitly in the DENSUM output file densum.lev, we eliminated this approximation and now simply use the eigenvalues as calculated. This change probably has very small effects on sums and densities of states, thermodynamic values, or rate constants.

7. BDENS and SCTST: improvements:
(a) Previously, these codes reported the zero point energy for the coupled degrees of freedom in the various output files, but did not include the separable degrees of freedom. This was inconvenient and could also lead to mistakes when using THERMO. The output has been revised in order to be more self-explanatory and to report the total ZPE, which includes ZPEs from both the coupled and the separable modes. (The ZPE of the un-bound reaction coordinate is not well-defined and is never included.)

(b) The temperature range of the vibrational partition functions has been extended down to 1 K (previously, the lower limit was 25 K). For the purpose of calculating thermodynamic functions and canonical (thermal) rate constants, these codes produce output files containing vibrational partition functions (from BDENS) or cumulative reaction probabilities (from SCTST) that can be used by THERMO. This method implements use of fully coupled anharmonic vibrational models. The temperature range was extended downward in order to facilitate analysis of low temperature experiments and astrophysical phenomena.

8. PARADENSUM: Revisions and New Features:
(a) The integer limit was sometimes exceeded when the flatness criterion was >99%. This problem has been fixed.

(b) To achieve better workload balance, a new keyword has been introduced: “windbal_key”. This new feature will speed up computation, but requires a small change to old data files.

(c) A more efficient starting point procedure has been introduced. This will speed up computation, but does not affect either the input or the output.

9. MULTIWELL USER MANUAL: The User Manual has been expanded to accommodate the new codes and re-structured to make it easier to use. Some other new sections have been added, including "1.2 How the Tools Work Together".