1.4 Modules and Their Functionality

For references see Bibliography.

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 [2–6] 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

perform (direct) SCF–HF and DFT calculations—as dscf and grad—within the very efficient RI–J approximation for the interelectronic Coulomb term. These programs also permit to approximate HF exchange within the RI–K approximation. The exchange correlation functionals supported are specified in define.
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 [10–17].

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):

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:

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 [20].

rirpa

calculates ground state energies and analytic first-order properties within the random phase approximation (RPA), see Section 12.

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  [21].

freeh

calculates thermodynamic functions from molecular data in a control file; an aoforce or a NumForce run is a necessary prerequisite.

intense

calculates Raman scattering cross sections from molecular data in a control file; an aoforce and an egrad run are a necessary prerequisite. Please use the Raman script to run these three steps in an automated way.

woelfling

computes a finite number of structures along reaction paths within different interpolation algorithms. It provides an initial path using a modified Linear Synchronous Transit. See Section 5.7 for details. Please use the woelfling-job script to run optimizations with it.