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multireference_rayleigh_schroedinger_perturbation_theory [2026/02/23 08:53] – [Multireference Rayleigh Schrödinger perturbation theory] wernermultireference_rayleigh_schroedinger_perturbation_theory [2026/02/27 10:46] (current) – fix broken link may
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   * **''SAVEH=''//record//** Record for saving the effective Hamiltonian in MS-CASPT2 calculations. If this is not given, a default record will be used (recommended).   * **''SAVEH=''//record//** Record for saving the effective Hamiltonian in MS-CASPT2 calculations. If this is not given, a default record will be used (recommended).
   * **''INIT''** (logical) Initializes a MS-CASPT2 with single state reference functions, see section [[multireference Rayleigh Schrödinger perturbation theory#Multi-State CASPT2|Multi-State CASPT2]]   * **''INIT''** (logical) Initializes a MS-CASPT2 with single state reference functions, see section [[multireference Rayleigh Schrödinger perturbation theory#Multi-State CASPT2|Multi-State CASPT2]]
-  * **''IGNORE''** (logical) Flags an approximate gradient calculation without CP-CASPT2; see section [[multireference Rayleigh Schrödinger perturbation theory**CASPT2 gradients|CASPT2 gradients]] for details.+  * **''IGNORE''** (logical) Flags an approximate gradient calculation without CP-CASPT2; see section [[multireference Rayleigh Schrödinger perturbation theory#CASPT2 gradients|CASPT2 gradients]] for details.
   * **''PROPERTIES''** or **''PROP''** (logical, default true, ''RS2C'' only) Flag on whether the expectation values of properties are computed. By default dipole moments are always computed but this may be expensive in multi-state calculations. Pass ''NOPROP'' to skip the property calculation.   * **''PROPERTIES''** or **''PROP''** (logical, default true, ''RS2C'' only) Flag on whether the expectation values of properties are computed. By default dipole moments are always computed but this may be expensive in multi-state calculations. Pass ''NOPROP'' to skip the property calculation.
  
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 ''STATE'',1,//root// ''STATE'',1,//root//
  
-where //root// is the desired root (i.e., 2 for the first excited state). In this case the Fock operator used in the zeroth-order Hamiltonian is computed using the density for the given state.+where //root// is the desired root (i.e., 2 for the first excited state). In this case the Fock operator used in the zeroth-order Hamiltonian is computed using the density for the given state. Note that all states must have the same symmetry.
  
 2) Alternatively, two or more states can be computed simultaneously, using 2) Alternatively, two or more states can be computed simultaneously, using
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 With the ''RS2C'' program the two modes can be mixed, e.g., in a 3-state calculation using the SS-SR-CASPT2 for one state and the MS-MR-CASPT2 for the other two states. With the ''RS2C'' program the two modes can be mixed, e.g., in a 3-state calculation using the SS-SR-CASPT2 for one state and the MS-MR-CASPT2 for the other two states.
 +
 +Note that all states must have the same spin and spatial symmetry.
 ==== Performing SS-SR-CASPT2 calculations ==== ==== Performing SS-SR-CASPT2 calculations ====
  
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 ===== Level shifts ===== ===== Level shifts =====
 +Note: level shifts have to be given as options. The SHIFT directive refers to denominator shifts, which affect the convergence but not the Hamiltonian and the results.
  
 Level shifts are often useful to avoid intruder state problems in excited state calculations. ''MOLPRO'' allows the use of shifts as described by Roos and Andersson, [[https://dx.doi.org/10.1016/0009-2614(95)01010-7|Chem. Phys. Lett.]] **245**, 215 (1995). The shift can be specified on the ''RS2'' or ''RS2C'' card Level shifts are often useful to avoid intruder state problems in excited state calculations. ''MOLPRO'' allows the use of shifts as described by Roos and Andersson, [[https://dx.doi.org/10.1016/0009-2614(95)01010-7|Chem. Phys. Lett.]] **245**, 215 (1995). The shift can be specified on the ''RS2'' or ''RS2C'' card