Note

This website is presently under development. The primary website for MOPAC is still http://openmopac.net until the majority of its contents have been migrated here.

INDO

Use the INDO/S (a.k.a. ZINDO/S) semiempirical model [13] instead of the default model, PM7 [19]. This INDO-based model is fit for spectroscopic applications, whereas all the other models available in MOPAC are based on the MNDO form [4] and fit for thermochemistry applications. A wide range of excited-state properties have been implemented in MOPAC’s INDO functionality [7], and it shares some features and keywords with the Multi-Electron Configuration Interaction capabilities of MOPAC. Ground-state properties (e.g. total energies, forces, vibrational frequencies, geometry optimization) are not available for INDO-based calculations.

The INDO-form Hamiltonian can be used with other parameters besides the default INDO/S model through the EXTERNAL keyword.

INDO-based calculations require the specification of an active space. The INDO/S model was originally fit for use with an active space of single-electron excitations (CIS). MOPAC’s implementation also allows for the use of double-electron excitations (CISD) and more general multi-reference active spaces (MRCI) to enable more accurate modeling of excited states with multi-electron excitation character.

INDO calculations in MOPAC are compatible with the COSMO solvation model [9], which enables the calculation of solvachromatic shifts. INDO calculations in MOPAC are incompatible with unrestricted orbitals (UHF) but compatible with restricted open-shell orbitals (RHF). Hoowever, the SCF convergence of open-shell RHF calculations may be poor.

The number of active configurations can be adjusted using MAXCI, C.I., C.I.D., and C.A.S.. The electron configurations used in INDO calculations are spin-adapted, and higher-spin states can be selected with their appropriate keyword (MS, DOUBLET, TRIPLET, etc.).