Analytical differentiation of the energy contribution due to triple excitations in fourth-order Møller-Plesset perturbation theory

✍ Scribed by Jürgen Gauss; Dieter Cremer

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 484 KB
• Volume: 153
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(88)80145-3

✦ Synopsis

Formulae for the analytical differentiation of the energy contribution due to triple (T) excitations within fourth-order Msller-Plesset (MP4) perturbation theory are derived. Combining these formulae with previously derived formulae for the evaluation of analytical first derivatives of the energy contributions due to single (S), double (D), and quadruple (Q) excitations at MP4

(Chem. Phys. Letters 138 ( 1987) 13 1 ), an algorithm is developed to calculate analytical MP4(SDTQ) energy gradients. Various ways of implementing this algorithm on a computer are discussed and the applicability of the corresponding computer programs is demonstrated by calculating equilibrium geometries, dipole moments, harmonic vibrational frequencies, and infrared intensities for some test molecules at the MP4 ( SDTQ ) level. The importance of triple excitations for an accurate description of multiple bonds is emphasized.