Accuracy and Efficiency
***********************

Given a Model Hamiltonian, the most important aspects determining the
accuracy of a Band calculation are:

* Basis set

* K-Space

Also important, but to a lesser degree, are the following aspects:

* Numerical Integration (BeckeGrid)

* Density fitting (ZlmFit)

* Basis-set confinement (SoftConfinement)

* SCF convergence (Convergence)

* Hartree–Fock Resolution of the Identity (RIHartreeFock) (only for
  hybrid functionals)

* For Many-body-perturbation theory (MBPT) options (only for MBPT
  calculations)

The CPU time and memory requirements strongly depend on these options,
as does the accuracy of the results.

**General NumericalQuality**

A simple way of tweaking the accuracy of the calculation is via the
**NumericalQuality** key. This sets the quality of several technical
aspects of a Band calculation (with the notable exception of the basis
set)

   NumericalQuality [Basic | Normal | Good | VeryGood | Excellent]

"NumericalQuality"
   Type:
      Multiple Choice

   Default value:
      Normal

   Options:
      [Basic, Normal, Good, VeryGood, Excellent]

   Description:
      Set the quality of several important technical aspects of a BAND
      calculation (with the notable exception of the basis set). It
      sets the quality of: BeckeGrid (numerical integration), ZlmFit
      (density fitting), KSpace (reciprocal space integration), and
      SoftConfinement (basis set confinement). Note: the quality
      defined in the block of a specific technical aspects supersedes
      the value defined in NumericalQuality (e.g. if I specify
      'NumericalQuality Basic' and 'BeckeGrid%Quality Good', the
      quality of the BeckeGrid will be 'Good')

* Basis set

  * Basis input block

  * Which basis set should I use?

  * Frozen core

  * Available Basis Sets

  * Pure STO and GTO basis sets

  * More Basis input options

  * Confinement of basis functions

  * Manually specifying AtomTypes (expert option)

  * Basis Set Superposition Error (BSSE)

  * Alternative elements / Virtual crystal approximation

* K-Space

  * KSpace input block

  * Recommendations for k-space

* Numerical Integration

  * Becke Grid

  * Radial grid of NAOs

  * Voronoi grid (deprecated)

* Density Fitting

  * Zlm Fit

  * STO Fit (Deprecated)

* Hartree–Fock RI

* Self Consistent Field (SCF)

  * SCF block

  * Convergence

  * DIIS

  * Multisecant

  * MultiStepper

  * DIRIS

* MBPT scheme

  * Recommended numerical settings

* More Technical Settings

  * Linear Scaling

  * Dependency

  * Screening

  * Direct (on the fly) calculation of basis and fit

  * Fermi energy search

  * Block size
