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Properties for Pseudopotentials: General Tips for Using the Databases

This guide teaches researchers how to locate some basic physical properties of elements and oxides, specifically required for generating and testing pseudopotentials.

Searching by Molecular Formula

Most information resources follow the Hill Order convention for writing molecular formula.  In it, you disregard functional or other units and simply deal with the composition of the substance.

  • Group all atoms of the same element together
  • Order the atomic symbols of the elements as follows
    • Organic Substances (defined as having at least one carbon atom): Carbon first, then hydrogen, then all other symbols in alphabetical order
    • Inorganic Substances (defined as having no carbon): All elements in alphabetical order

This means that the formula for sodium chloride will look strange (ClNa), but it is the most effective way of finding substances in all resources.

The Inorganic Crystal Structure Database (ICSD) is a little different, in that it has no "molecular formula" field.  Instead, you use the composition field, where you do want to write the formula according to structural units.

General Pointers for Searching in SciFinder

SciFinder is not a properties database, like Reaxys and the CRC Handbook, but it does include the CAS Registry, a listing of all substances published in the literature (and a few that were not) since the late 1960s.  Currently there are almost 7 million substances included in the Registry, and some of them have property information as part of their records.

You will want to begin your search from the Substances context.  From here, you can choose whether to search by structure, formula, or substance identifier (name or CAS Registry Number).  It is best to search for elements, oxides, and diatomics either by formula or by name.  When performing a formula search, make sure that all like atoms are grouped together.  SciFinder is not terribly strict about Hill Order, but you should make an effort.

 

When you retrieve your results, it will order them according to CAS Registry Number.  It is frequently helpful to resort them by number of references, since the most reference substance is usually the one that you need.  You can also refine them to exclude isotope-containing substances, which can cut down on your results.

From the brief result view, you can click on the substance's Registry number to get to the full record for that substance, or you can click on the Key Physical Properties link to see the properties available for that substance.

General Pointers for Searching in Knovel

For the most part, it is easier to find properties in Knovel using the Material Property Search (previously known as data search form), rather than performing a keyword search through the full text of the books.  However, if you cannot find what you need using the data search, the keyword search can be a good way of double-checking to make sure that you are not missing anything, as data search tends to focus on tables of information in reference books.

Click on the Material Property Search option in the top menu bar to begin your data search.  Once in the Material Property Search Interface, you need to select the fields in which to search, as well as any particular values you wish to find in these fields.

1. Use the query builder for your search. Click and drag the property types from the left-hand side menu to the center of the screen.

  • Search by material or substance name, by property, or by both.
  • To search by material or substance, enter a material or substance name into the 'Material or Substance Name' field.
  • To search by properties, drag and drop, or double-click the property into the query builder. You can find the property by either:
  • Browsing the Properties list.
  • Entering a name into the ‘Find a property’ search box. As you type, property names are filtered from the list.

2. Use operators to further specify your search.

  • Knovel allows you to use the following numeric operators:
  • Exists: the table or graph contains data for that property
  • Equals (=)
  • Less than or equal to (<=)
  • Greater than or equal to (>=)
  • Is between (>=/<=)
  • You can enter numeric values or numeric ranges.
  • You can select units of measurements using the drop-down menu.
  • You can combine up to three properties in the query builder using ‘AND’, ‘OR’ and ‘NOT’ operators.

3. Click 'Results' in the lower right-hand corner to run your search.