Sources of reference data are given by mnemonics. All references are in a single file, REFERENCES, which connects a mnemonic with the text of the reference. Consider water:
SYMMETRY Water I=12.62 D=1.85 H=-57.8 HR=JANAF86 DR=NLM1967 IR=TBBB1970 H 0.00000000 +0 0.0000000 +0 0.0000000 +0 O 0.94908848 +1 0.0000000 +0 0.0000000 +0 1 0 0 H 0.94908848 +0 107.5378048 +1 0.0000000 +0 2 1 0 2 1 3
The heat of formation reference is JANAF86. In REFERENCES, JANAF86 refers to "M. W. Chase, C. A. Davies, J. R. Downey, D. R. Frurip, R. A. McDonald, A. N. Syverud, JANAF Thermochemical Tables, Third Edition, J. Phys. Chem. Ref. Data 14, Suppl. 1 (1985)." Similarly, the dipole mnemonic is NLM1967, which refers to "R. D. Nelson, D. R. Lide, A. A. Maryott, Nat. Stand. Ref. Data Set., Natl. Bur. Stand. No. 10 (1967)." Reference mnemonics can be up to 8 characters long.
If the value of a reference datum is questioned, then the accuracy of the new value can be compared to that of the current reference value, using the source of the current reference value. References are also used in preparing tables. If a new reference is used, REFERENCES should be updated to include the new reference and a mnemonic created to allow it to be used in reference data sets.
HR=REF: This reference indicates that the heat of formation is to be calculated, but not used in parameter optimization or in the tables. Such data are however used as reference data in functions.
HR=GUESS: The heat of formation is to be used in parameterization but not used in surveys, unless the job uses keyword "ALL".
HR=DUMMY: This is an intelligent guess as to the value of the heat of formation.