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the_scf_program [2025/09/24 14:44] – update spin+irrep dollthe_scf_program [2025/09/25 13:22] (current) – RHF only high-spin doll
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 Note that these values take sensible defaults if any or all are not specified (see section [[general program structure#symmetry|symmetry]]). For example, ''%%{rhf; wf,sym=N,spin=M}%%'' gives the explicit values N for the symmetry and M for the spin of the wave function, but uses the default number of electrons. Note that these values take sensible defaults if any or all are not specified (see section [[general program structure#symmetry|symmetry]]). For example, ''%%{rhf; wf,sym=N,spin=M}%%'' gives the explicit values N for the symmetry and M for the spin of the wave function, but uses the default number of electrons.
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 +In HF/RHF, the spin has to be equal to the number of singly occupied orbitals, i.e. the electrons couple to a high-spin state. For example, an open-shell singlet state cannot be described on this level. Instead, for states which are not high-spin, MCSCF has to be used.
  
 ==== Defining the number of occupied orbitals in each symmetry ==== ==== Defining the number of occupied orbitals in each symmetry ====
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   * Whether your geometry is sensible (e.g., look for Angstrom/Bohr conversion issues). Note that Molpro prints bond distances in both Angstroms and atomic units at the top of an output.   * Whether your geometry is sensible (e.g., look for Angstrom/Bohr conversion issues). Note that Molpro prints bond distances in both Angstroms and atomic units at the top of an output.
-  * Whether you have selected the correct electronic state (spin and symmetry). Molpro tries to guess spatial symmetries of open-shell compounds automatically if none are provided. However, the guess is not always right. In such a case you need to give the symmetry manually (in the simplest case as ''%%wf,sym=N,spin=M%%''. See section [[the SCF program#defining the wavefunction|defining the wavefunction]]). Molpro does //not// attempt to guess the spin state of the input compound automatically; it defaults to spin=0 for systems with even numbers of electrons and spin=1 for odd-numbered species.+  * Whether you have selected the correct electronic state (spin and symmetry). Molpro tries to guess spatial symmetries of open-shell compounds automatically if none are provided. However, the guess is not always right. In such a case you need to give the symmetry manually (in the simplest case as ''%%wf,sym=N,spin=M%%''. See section [[the SCF program#defining the wavefunction|defining the wavefunction]]). Molpro does attempts to find the ground state configuration from the Aufbau principle, but this may fail and then the wave function symmetry and spin need to be specified using a WF (wave function) directive
  
 If convergence problems persist, it is recommended to use the new mixed first-order/second-order MCSCF program (''%%MULTI,SO-SCI%%'', or (recommended for larger systems) ''%%DF-MULTI%%'' (SO-SCI is default for DF-MULTI) as described in D.A. Kreplin, P.J. Knowles and H.-J. Werner, J. Chem. Phys. 152, 074102 (2020); https://doi.org/10.1063/1.5142241. This provides very robust convergence, even in cases where RHF does not converge or converges to a wrong solution. Due to faster convergence and only small additional cost per iteration the overall computation time is often even smaller than for conventional RHF or DF-RHF. For MULTI it is necessary to specify the configuration uniquely using OCC, CLOSED, and WF directives. If convergence problems persist, it is recommended to use the new mixed first-order/second-order MCSCF program (''%%MULTI,SO-SCI%%'', or (recommended for larger systems) ''%%DF-MULTI%%'' (SO-SCI is default for DF-MULTI) as described in D.A. Kreplin, P.J. Knowles and H.-J. Werner, J. Chem. Phys. 152, 074102 (2020); https://doi.org/10.1063/1.5142241. This provides very robust convergence, even in cases where RHF does not converge or converges to a wrong solution. Due to faster convergence and only small additional cost per iteration the overall computation time is often even smaller than for conventional RHF or DF-RHF. For MULTI it is necessary to specify the configuration uniquely using OCC, CLOSED, and WF directives.