Read Me

premdb 1.0                                              Stefan Revets, May 2010

          INTRODUCTION

Premdb is a package written to obtain various thermodynamic properties for
a number of minerals. The basic calculations have been carried out with
Perple_X (written by J. Connolly), using the thermodynamic database of 
Holland and Powell (2002). Thermodynamic properties of interest are
extracted from the database with the WERAMI program, part of the Perple_X
package.


          REQUIREMENTS

Premdb is written in Python 2.5 on a GNU/linux system. It requires the
presence of werami somewhere on the system.


          INSTALLATION

It would be best to install the premdb database in a location where users
have write permissions (or a premdb group with write permissions can be 
created). Premdb assumes that the data files are installed in the directory
/usr/local/share/premdb/data. Another location is perfectly acceptable,
as long as an environmental variable PREMDB is set to point to it.


          USING premdb

Premdb is a command-line driven program. Arguments and options can be given
on the command line, or can be written in separate text files. An overview
of the options is given by 

     premdb -h|--help. 

The minimal input for premdb is a mineral name and a thermodynamic property. 
A list of available minerals and properties (with the required case-sensitive
spelling) can be called up by

     premdb -l|--list minerals|properties

The format of a text file, rather than command line options, to direct 
premdb is straightforward. Options and requests can be listed in any order, 
one option per line, and each line (including the last one!) ending with 
a single new-line. Options are announced by their key word, followed by the 
choses value.
For example:

     mineral q
     property poisson
     temperature 300 1000 50
     pressure 10 1000 100
     operation nonlinear_geotherm
     polynomial 10 0.03 0.005 -0.23
  
which yields the poisson ratio of quartz along a P-T path defined by the
polynomial (maximum order 10) so that 

     P = sum ( c_i * T^i )  0 < i < n

Other possible choices for operation include linear_geotherm and datamatrix,
both of which do not use a polynomial.
The temperature and pressure limits do not have to be defined: in that case
the default values of 300 to 1300 K with 200 steps and 0.1 to 3000 MPa  with
300 steps will be used. The minimum temperature and pressure can be higher 
than the maximum, representing a cooling/exhumation path. However, their
values cannot go beyond the default values.

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Update 26 July 2010

There is a problem with the elastic properties of quartz in the
Holland and Powell database as used by Perple_X, and thus premdb.

The alpha-beta transition in quartz is modelled as a Landau transition,
and implemented by the addition of Gibbs Free Energy. This works fine
for most thermodynamic properties, but because of the very peculiar
nature of quartz, it does not work for the bulk modulus, and related
elastic properties.

In premdb, the issue has been addressed by setting alpha quartz as the
default (including elastic properties), which means that elastic
properties (and only elastic properties) of beta quartz will be wrong.
If these are required, you can request the properties for betaq, rather
than q.