Orbital Handling and Localization Settings

Convergence difficulties can be encountered when orbitals of different symmetries swap. You can fix the population in each symmetry by selecting Fixed symmetry populations.1 Keyword ipopsym=1 in the gen section. This option is useful when you are running calculations on different occupations of degenerate d orbitals, or if you want to converge on a state that is not the ground state but can be distinguished by the occupations of orbitals of different symmetries.

When running calculations on a set of isomeric structures, the results may depend on the number of canonical orbitals used for each isomer. If they are different, the results are not strictly comparable. You can enforce the same number of canonical orbitals for each isomer by selecting Use consistent orbital sets when all input structures are isomers. An initial one-electron integral calculation is run on each isomer to determine the number of canonical orbitals, and the minimum number is selected and enforced for all subsequent steps of the job.

By default, the final wave function is not localized.2 Keyword locpostv = 0 in the gen section. You can localize the valence orbitals after the wave function is computed with either the Boys3 Keyword locpostv = 1 in the gen section. procedure [97] or the Pipek-Mezey4 Keyword locpostv = 2 in the gen section. procedure [98], by choosing from the Final localization option menu. The Boys procedure localizes the doubly-occupied orbitals by maximizing the term . Pipek-Mezey localization is performed by maximizing the sum of the squares of the atomic Mulliken populations for each atom and occupied orbital. See Jaguar Output Options for Orbitals to find out how to print the localized orbitals resulting from either method.

Both of the available localization methods scale as N³ with basis set size. However, the use of molecular symmetry is turned off for the entire job whenever you perform a final localization, so for faster results you might want to run a job without localization, then restart the job after turning on localization in the new input file. See Restarting Jaguar Jobs and Using Previous Results for information on restart files and restarting jobs.