Modules and Their Functionality

`define`- interactive input generator which creates the
input file
`control`.`define`supports most basis sets in use, especially the only fully atom optimized consistent basis sets of SVP and TZV quality [2,3,4,5,6] available for the atoms H-Rn, excluding lanthanides.`define`determines the molecular symmetry and internal coordinates allowing efficient geometry optimization.`define`allows to perform a geometry optimization at a force field level to preoptimize the geometry and to calculate a Cartesian Hessian matrix.`define`sets the keywords necessary for single point calculations and geometry optimizations within a variety of methods. There are also many features to manipulate geometries of molecules: just try and see how it works. `uff`- performs a geometry optimization at a force field
level. The Universal Force Field (UFF) [7] is
implemented. Beyond this it calculates an analytical Hessian
(Cartesian) which will be used as a start Hessian for an
*ab initio*geometry optimization. `dscf`- for (semi-)direct SCF-HF and DFT calculations (see
keywords for functionals supported).
`dscf`supports restricted closed-shell (RHF), spin-restricted ROHF as well as UHF runs.`dscf`includes an in-core version for small molecules. `grad`- requires a successful
`dscf`run and calculates the gradient of the energy with respect to nuclear coordinates for all cases treated by`dscf`. `ridft`

and`rdgrad`

`mpgrad`- requires a well converged SCF
run--by
`dscf`, see keywords--and performs closed-shell RHF or UHF calculations yielding single point MP2 energies and, if desired, the corresponding gradient. `rimp2`- calculates MP2 energies and
gradients for RHF and UHF wavefunctions, significantly more
efficient than
`mpgrad`by using the RI technique [8,9]. `ricc2`- calculates electronic excitation
energies, transition moments and properties of excited states at the
CIS, CIS(D), ADC(2) and CC2 level using either a closed-shell RHF or
a UHF SCF reference function. Calculates R12 basis set limit
correction for MP2 energies. Employs the RI technique to
approximate two-electron integrals.
Includes as a subset also the functionalities of the
`rimp2`program [10,11,12,13]. `relax`- requires a gradient run--by
`grad`,`rdgrad`,`rimp2`or`mpgrad`--and proposes a new structure based on the gradient and the approximated force constants. The approximated force constants will be updated. `statpt`- performs structure optimization using the "Trust Radius Image Minimization" algorithm. It can be used to find minima or transition structures (first order saddle points). Transition structure searches usually require initial Hessian matrix calculated analytically or the transition vector from the lowest eigenvalue search.
`frog`- executes one molecular dynamics (MD) step. Like
`relax`, it follows a gradient run: these gradients are used as classical Newtonian forces to alter the velocities and coordinates of the nuclei. `aoforce`- requires a well converged SCF or DFT run--by
`dscf`or`ridft`, see keywords--and performs an analytic calculation of force constants, vibrational frequencies and IR intensities.`aoforce`is also able to calculate only the lowest Hessian eigenvalues with the corresponding eigenvectors which reduces computational cost. The numerical calculation of force constants is also possible (see tool`Numforce`in Section 1.5). `escf`- requires a well converged SCF or DFT run and
calculates time dependent and dielectric properties (spin-restricted
closed-shell or spin-unrestricted open-shell reference):
- -
- static and frequency-dependent polarizabilities within the SCF approximation
- -
- static and frequency-dependent polarizabilities within the
time-dependent Kohn-Sham formalism, including hybrid functionals

such as B3-LYP - -
- electronic excitations within the RHF and UHF CI(S) restricted CI method
- -
- electronic excitations within the so-called SCF-RPA approximation (poles of the frequency dependent polarizability)
- -
- electronic excitations within the time dependent Kohn-Sham formalism (adiabatic approximation). It can be very efficient to use the RI approximation here, provided that the functional is of non-hybrid type: we recommend B-P86 (but slightly better results are obtained for the hybrid functional B3-LYP) [14].
- -
- stability analysis of single-determinant closed-shell wave functions (second derivative of energy with respect to orbital rotations) [15].

`egrad`- computes gradients and first-order properties of
excited states. Well converged orbitals are required. The following
methods are available for spin-restricted closed shell or
spin-unrestricted open-shell reference states:
- -
- CI-Singles approximation (TDA)
- -
- Time-dependent Hartree-Fock method (RPA)
- -
- Time-dependent density functional methods

`egrad`can be employed in geometry optimization of excited states (using`jobex`, see Section 5.1), and in finite difference force constant calculations (using`Numforce`). Details see [16]. `mpshift`- requires a converged SCF or DFT run for closed
shells.
`mpshift`computes NMR chemical shieldings for all atoms of the molecule at the SCF, DFT or MP2 level within the GIAO ansatz and the (CPHF) SCF approximation. From this one gets the NMR chemical shifts by comparison with the shieldings for the standard compound usually employed for this purpose, e.g. TMS for carbon shifts. Note that NMR shielding typically requires more flexible basis sets than necessary for geometries or energies. ECPs are not supported in`mpshift`[17]. `freeh`- calculates thermodynamic functions
from molecular data in a
`control`file; an`aoforce`or a`NumForce`run is a necessary prerequisite.