Energy and Gradient Calculations

Energy calculations may be carried out at different levels of theory.

Hartree-Fock-SCF

use modules DSCF and GRAD to obtain the energy and gradient. The energy can be calculated after a DEFINE run without any further keywords or previous runs. The gradient calculation however requires a converged DSCF run.

Density functional theory

DFT calculations are carried out in exactly the same way as Hartree-Fock calculations except for the additional keyword $dft. For DFT calculations with the fast Coulomb approximation you have to use the modules RIDFT and RDGRAD instead of DSCF and GRAD. Be careful: DSCF and GRAD ignore RI-$K$ flags and will try to do a normal calculation, but they will not ignore RI-$J$ flags ($rij) and stop with an error message. To obtain correct derivatives of the DFT energy expression in GRAD or RDGRAD the program also has to consider derivatives of the quadrature weights--this option can be enabled by adding the keyword weight derivatives to the data group $dft.

Excited states

Single point excited state energies for CIS, TDHF and TDDFT methods can be calculated using ESCF. Excited state energies, gradients, and other first order properties are provided by EGRAD. Both modules require well converged ground state orbitals.

MP2

the module MPGRAD calculates the MP2 energy as well as the energy gradient. If only the energy is desired use the keyword $mp2energy. MP2 calculations need well converged SCF runs (the SCF run has to be done with at least the density convergence $denconv 1.d-7, and $scfconv 6 as described in Section 12). For all further preparations run the tool MP2PREP. For MP2 calculations in the RI approximation use the RICC2 module. The input can be prepared with the cc2 menu in DEFINE. (Alternatively, the older RIMP2 module and for preparation of its input the tool RIMP2PREP maybe used).

CC2

the moldule RICC2 calculates MP2 and CC2 ground state energies and CIS/CCS, CIS(D) or CC2 excitation energies using the resolution-of-the-identity (RI) approximation. Gradients are available for ground states the MP2 and CC2 and for excited states at the CC2 level. In addition transition moments and first-order properties (for ground and excited states) are available for some of the methods. For more details see Section 7. The RICC2 module requires are well converged SCF moleculare orbitals. The input can be prepared using the cc2 menu of DEFINE.

For a semi-direct DSCF calculation (Hartree-Fock or DFT) you first have to perform a statistics run. If you type

stati dscf
nohup dscf > dscf.stat &

the disk space requirement (MB) of your current $thime and $thize combination will be computed and written to the data group $scfintunit size=integer (see Section 12.2.5). The requirement of other combinations will be computed as well and be written to the output file dscf.stat.