# Parameter describing calculations

## calculation.name

**keyword**: calculation.name

**possible values**: one from the following list, or a cell array with
each cell containing one from the following list.

init, initial, initialize, initialization;

NSC, NSCF, nonSelfConsistentField, rigidAtomicField, neutralAtomicPotential;

HarrisField, HarrisEnergyFunctional, HarrisFunctional, HarrisEnergy, Harris, HarrisApproximation;

SC, SCF, selfConsistentField, selfConsistent;

PSC, PSCF, PostSCF, postField, postSelfConsistencyField, postSelfConsistentField;

TE, totalEnergy, energy;

TP, P, momentum;

force;

stress, stressMatrix;

Hessian, HessianMatrix, dynamicalMatrix;

BS, bandStructure;

CBS, complexBandStructure

FBS, fullBandStructure, fermiSphere, fermiSurface

eig, eigs, eigen, eigenStates;

SS, scatteringStates;

DOS, densityOfStates;

DOSS, densityOfScatteringStates;

CH, charge, electron, electrons;

PO, potential;

EPhCoupling;

TR, TM, transmission;

TRC, TMC, channel, transchannel, transmission-channel, transmissionchannel;

CO, COND, conductance;

ACCO, ACCOND, acConductance;

IVC, IVCurve;

IETS;

relax, relaxation, structureRelaxation;

basisOptimization, BO;

**default value**: no default value, must be provided.

**description**: The above list of possible values are divided into
groups by ;. Values in the same group are all
equivalent, i.e. they invoke the same calculation.

Note that when choosing more than one calculation, they must be arranged in a physically correct (meaningful) order.

The following are descriptions of each calculation.

initialization : for construction of the system object without calculating any physical property.

rigidAtomicField : a simple summation of precalculated atomic self-consistent fields of all atoms involved in the system without any further electronic relaxation. This calculation generates the Hamiltonian and the real space charge density needed for further calculations. This field or potential is not self-consistent. In a DFT calculation, this field accounts for those terms of the Hamiltonian that need to be computed only once outside of the self-consistent loop.

HarrisField : same as the rigidAtomicField calculation but within the Harries functional method. The Harris total energy is an approximation of the DFT self-consistent total energy.

The HarrisField calculation can also be used together with the SCF option. After 2 or 3 self-consistent steps (by setting calculation.SCF.maximumSteps = 2 or 3), the estimation of total energy may be somewhat improved.

SCF : generates Hamiltonian and density which are consistent with each other.

PostSCF : modify the (self-consistent) Hamiltonian by various additional terms, e.g. the terms caused by an applied external magnetic field.

totalEnergy: the total energy of the system as defined by the density-functional theory. The total energy can also be decomposed into several terms, like kinetic energy, band structure energy, short range energy, and so on.

momentum: calculate total electronic momentum of the system and also the electronic momentum matrix.

force: atomic forces, which can also also be decomposed into several terms, like kinetic force, short range force, and so on.

stress: the stress tensor of the system, which is defined as the negative derivative of the total energy with respect to the strain tensor. The stress tensor can also be decomposed into several terms, like kinetic stress, short range stress, and so on.

hessian: the hessian matrix, which is defined as the second derivative of the total energy with respect to atomic positions.

The corresponding dynamical matrix can also be calculated, with which the phonon spectrum and vibrational modes of the system can further be determined.

In addition, the derivative of the Hamiltonian matrix with respect to atomic positions can also be calculated, which could be used to study the phonon and electron interactions.

bandStructure: the normal band structure calculation which gives the band energies as a function of a series of k-points. The k-points are normally along a line segment(s) in the k-space.

complexBandStructure: the complex-band structure calculation. Comparing to normal band structure which displays a band energy as a function of a k-point, i.e., e = e(k1,k2,k3), the complex-band structure displays a k-coordinate, e.g. k3, as a function of band energy and other k-coordinates, i.e., k3 = k3(e;k1,k2) where the value of k3 is normally a complex number.

fullBandStructure: this calculation gives the band energies at all k-points whin the Brillouin zone. The fermi surface can also be determined and visualized, with which electronic transmission properties of a lead can be studied.

eigenStates: this calculation is used for molecular or periodic bulk systems, which gives eigen energies and also corresponding wave functions as a vector of the coefficients of a set of atomic basis and/or as a real-space function, for a set of states specified by an user.

scatteringStates: this calculation is used for systems with probes, which gives transmission and reflection coefficients and also the real-space wave function, for a set of states specified by an user.

densityOfStates: the density of electronic states (dos), which can also be decomposed in various ways to obtain projected dos, local dos, and so on.

densityOfScatteringStates: the density of electronic scattering states (dos), which can also be decomposed in various ways to obtain projected dos, local dos, and so on. Comparing to the normal dos, doss only counts for the scattering states associated to a specific lead and washes out all other states.

charge: analysis of the total charge of the system in various ways, such as projected to some particular atomic orbitals, localized to a particular real-space region, projected to the spin-polarization direction, and so on.

potential: this calculation is to obtain and also display or visualize a real-space potential function of Vdh, Vxc, Vna, or Veff, where Vdh is the delta_Hartree potential, Vxc is the exchange-correlation potential, Vna is the neutral atomic potential, and Veff = Vdh+Vxc.

Note that the difference of two Vdh calculated with and without a bias voltage gives the detailed information about how the voltage drops across the structure.

EPhCoupling: the electron-phonon couplings.

transmission: transmission coefficients calculation, which can be used to determine the conductance of the structure.

channel: the number of transmission channels of a system when being used as a lead, which is given as a function of energy, transverse wave vectors.

conductance: the conductance. The current with the applied voltage is also calculated.

acConductance: the ac conductance when an ac bias voltage is applied.

IVCurve: this calculation gives the current as a function of applied voltages, and the intermediate data of conductance is also given.

IETS: The inelastic electron tunneling spectroscopy.

relaxation: structure relaxation with or without change of the central cell. Various constrains can be applied during the relaxation.

basisOptimization: used to optimize the atomic basis for a particular system(s). This is normally a key step to a reliable result with high precision.

**an example**:

```
calculation.name = {scf, bs}
```