■ HOW MOLCALC WORKS
MolCalc is split into two steps: building the molecule and calculating molecule properties. The editor is centered around
the JSmol4 plugin, which is a new JavaScript version of the popular Jmol5 visualization program that, unlike Jmol, works on a broad range of devices without the use of Java, such as the iPhone and iPad. Different starting structures are provided, as well as the possibility to search for other structures using common names or SMILES.6 The Chemical Identifier Resolver is used for searching and naming of structures.7 The editor interface is based on a point-and-click approach with a clear intuitive workflow, as seen in Figure 1. JSmol is used for all molecule modifications as well as structure minimization using the MMFF force field.8
In the Molecule Calculator page, the structure is reoptimized at the PM3 level of theory9 for a maximum of 50 steps, using the GAMESS program.10 After the minimization, the student is presented with the PM3 minimized structure and the different calculation types. The PM3 structure can then be used to compute the heat of formation and other thermodynamic properties, vibrational frequencies and normal modes at the PM3 level of theory, or the molecular orbitals and orbital energies using the RHF/STO-3G level of theory. PM3 reproduces experimental heats of formation with an average error of 7.8 kcal/mol.11 Thus, heats of formation of elements in their standard state can be significantly difference from zero. Vibrational frequencies computed with PM3 have errors of ca. 160 cm−1.12 These cal-culations are also performed with the GAMESS program. OpenBabel13 is used to manage input and coordinate files.
To ensure a fast turnaround, MolCalc allows calculations on (closed shell) molecules with only doubly occupied molecular orbitals and with less than 11 non-hydrogen atoms. Only elements