Gaussian 03 Online ManualLast update: 2 October 2006 | |

## ForceThis calculation type keyword requests a single calculation of the forces on the nuclei (i.e., the gradient of the energy). The dipole moment is also computed (as a proper analytic derivative of the energy for MP2, CC, QCI and CI) [202,447].
Analytic gradients are available for all SCF wavefunctions, all DFT methods, CIS, MP2, MP3, MP4(SDQ), CID, CISD, CCD, CCSD, QCISD, CASSCF, SAC-CI and all semi-empirical methods. For other methods, the forces are determined by numerical differentiation. The forces on the nuclei appears in the output as follows (this sample is from a calculation on water): ***** AXES RESTORED TO ORIGINAL SET ***** ------------------------------------------------------------------- Center Atomic Forces (Hartrees/Bohr) Number Number X Y Z ------------------------------------------------------------------- 1 8 -.049849321 .000000000 -.028780519 2 1 .046711997 .000000000 -.023346514 3 1 .003137324 .000000000 .052127033 ------------------------------------------------------------------- MAX .052127033 RMS .031211490 ------------------------------------------------------------------- Internal Coordinate Forces (Hartree/Bohr or radian) Cent Atom N1 Length/X N2 Alpha/Y N3 Beta/Z J ------------------------------------------------------------------- 1 O 2 H 1 -.023347( 1) 3 H 1 -.023347( 2) 2 -.088273( 3) ------------------------------------------------------------------- MAX .088272874 RMS .054412682 The forces are determined in the standard orientation, but are restored to the original (Z-matrix) set of axes before printing (as noted in the output). This is followed by the corresponding derivatives with respect to the internal coordinates (lengths and angles used in the Z-matrix) when internal coordinates are in use. The forces are followed in each case by their maximum and root-mean-square values. |