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general_hints_-_frequently_asked_questions [2025/07/10 11:48] – [In a nutshell: how to start] dollgeneral_hints_-_frequently_asked_questions [2026/03/30 11:37] (current) – [Geometry] doll
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 One should start with a basic input and then gradually increase complexity; it is not a good idea to start with One should start with a basic input and then gradually increase complexity; it is not a good idea to start with
 a complicated input and then change input parameters without any knowledge what these parameters are meant for. a complicated input and then change input parameters without any knowledge what these parameters are meant for.
 +Break problems into small pieces, and try to solve the smaller problems.
  
 A more extended introduction how to use Molpro is in [[quickstart|this section of the manual]]. A more extended introduction how to use Molpro is in [[quickstart|this section of the manual]].
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   * Computational parameters such as tolerances, thresholds have been carefully calibrated. Usually they do not need to be changed.   * Computational parameters such as tolerances, thresholds have been carefully calibrated. Usually they do not need to be changed.
-  * gprint,basis,orbitals may be inserted so that these data are available in the output file; it however makes the output file larger.+  * ''gprint,basis,orbitals,civector'' may be inserted so that these data are available in the output file; it however makes the output file larger. Use e.g. ''gprint,orbitals=2'' to print occupied and two lowest virtual orbitals
   * Molpro uses a default memory size [[general_program_structure#memory_allocation|(see here)]] which should be sufficient for small systems. When requesting more memory, it is recommended to first get some experience about the memory necessary, and then request a reasonable amount of memory, and not astronomic memory for small systems.   * Molpro uses a default memory size [[general_program_structure#memory_allocation|(see here)]] which should be sufficient for small systems. When requesting more memory, it is recommended to first get some experience about the memory necessary, and then request a reasonable amount of memory, and not astronomic memory for small systems.
 ==== Geometry ====   ==== Geometry ====  
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   * The units have to be correct (Angstrom versus bohr). By default, xyz input is in Angstrom, while z-matrix coordinates are in atomic units.     * The units have to be correct (Angstrom versus bohr). By default, xyz input is in Angstrom, while z-matrix coordinates are in atomic units.  
   * A geometry which strongly deviates from the experimental geometry may cause convergence problems. This may be due to unrealistic bond lengths or angles. E.g. breaking a bond may require to change the wave function card or method (remember the text book example of H<sub>2</sub> with a large bond length, RHF versus UHF).     * A geometry which strongly deviates from the experimental geometry may cause convergence problems. This may be due to unrealistic bond lengths or angles. E.g. breaking a bond may require to change the wave function card or method (remember the text book example of H<sub>2</sub> with a large bond length, RHF versus UHF).  
-  * If any kind of problems in a calculation occur, it is recommended to visualise the geometry and check it for correctness.  +  * If any kind of problems in a calculation occurs, it is recommended to visualise the geometry and check it for correctness.  
      
 ==== Basis set ==== ==== Basis set ====
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 +==== molpro not running ====
  
 +If molpro is in the path, but not properly running, then
 +''molpro -v''
 +may help to get information about what goes wrong.
 ==== Hardware ==== ==== Hardware ====