Comments and suggestions about HPDF keywords - pdera/HPDF-file-format GitHub Wiki

Among things we should add to the HPDF format are uncertainties (e.g. for cell parameter, bulk moduli, thermal expansivities, etc.)

Thus far, we have not been able to store some information that is very relevant:

*Linear compressibilities

*Linear thermal expansivities

*Pressure and temperature dependencies of unit cell angles (e.g. monoclinic beta angle), which are usually not described by EoS formulations (but e.g. polynomial fits).

All of the above affect peak positions at high P and T and are currently ignored.

Right now the JCPDS keyword names are strings composed of only common characters, and terminated with a colon. It seems that we need a little more hierarchical complexity: Looking at JCPDS version 4 it seems to me that we have 3 categories of keywords:

  1. Special keywords – no need to specify uncertainties or source
  2. Thermoelastic keywords – each parameter should have associated keywords specifying both uncertainty and source. Most of these will have associated keywords specifying P and T dependencies (which also require additional associated keywords specifying uncertainty and source). For most of these there may (or may not) be a need to specify definition/equation type (e.g. EoS type)
  3. Diffraction keywords –describe diffraction peaks. For intensity and hkls no need to specify uncertainties or source. There may be one or few additional keywords for the whole diffraction category to describe what type of intensity calculation method was used, what was the wavelength to calculate intensities, name/link to a cif file used to calculate intensity, min intensity cutoff, etc.

We may want to include more categories.

Maybe we could introduce new keywords that use special characters to emphasize hierarchy of keyword dependencies, the way that e.g. CIF format does this:

VOLUME0: 254.2

VOLUME0_sig: 0.2

VOLUME0_source: Shim et al. (2010) Amr. Mineral 1, 001-002

VOLUME0_method: Rietveld refinement

VOLUME0_unit: A^3

K0: 164.2

K0_sig: 0.3

K0_source: Shim et al. (2010) Amr. Mineral 1, 001-002

K0_type: BM3

K0_unit: GPa

K0_method: DFT_GGA

K0_DP: 4.2

K0_DP_sig: 0.3

K0_DP_source: Shim et al. (2010) Amr. Mineral 1, 001-002

K0_DP_method: DFT_GGA