On the First‐Order Correction for One‐Body Properties in Uncontracted Multireference Perturbation Theory Framework

The first‐order correction for the one‐body electronic properties can be a powerful tool for increasing the accuracy of their calculations in the framework of multireference perturbation theory (MRPT) methods. The individual contributions for the evaluation of the one‐body properties are derived for the fully uncontracted MRPT. A detailed algorithm for their simple and cost‐effective calculation is also presented. A way to construct a sum of zeroth‐ and first‐order contributions in operator form is demonstrated. Results obtained in the framework of uncontracted MRPT CDAS‐PT2(IPEA) implemented in the NOPT quantum chemistry package for test cases of several small molecules show the improvement of the precision of the calculation for the permanent and transition dipole moment.