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the_nevpt2_program [2026/02/26 10:38] – update examples maythe_nevpt2_program [2026/02/27 07:27] (current) – [Input description] werner
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 An example is provided where the energies of the ground state and of the first $^1A_2$ ($n \to \pi^*$) excited state of formaldehyde are calculated. An example is provided where the energies of the ground state and of the first $^1A_2$ ($n \to \pi^*$) excited state of formaldehyde are calculated.
 +
 +The first example shows a detailed input, where occupations, spatial and spin symmetries, and orbital orbital records are given explicitly in each step. This input can be much simplified by using defaults: the NEVPT2 program (as also other correlation programs) automatically use the same occupations, symmetries and orbitals as in the previous CASSCF orbital optimisation. The third example uses density fitting approximations for the integrals, which is strongly recommended for larger molecules.
  
 <code - examples/form_nevpt2.inp> <code - examples/form_nevpt2.inp>
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 } }
 </code> </code>
 +
 +Simplified input:
 <code - examples/form_nevpt2_simple.inp> <code - examples/form_nevpt2_simple.inp>
 geometry geometry
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 nevpt2 nevpt2
 </code> </code>
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 +Calculation with density fitting:
 <code - examples/form_dfnevpt2.inp> <code - examples/form_dfnevpt2.inp>
 geometry geometry