CASINO manual - Theory of Condensed Matter
CASINO manual - Theory of Condensed Matter
CASINO manual - Theory of Condensed Matter
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ESUPERCELL (Logical) By default total energies and their components in periodic systems are<br />
printed as energies per primitive cell. Switching this flag to T forces printing <strong>of</strong> energies per<br />
simulation cell in the output file.<br />
EWALD CHECK (Logical) casino and the wave-function generating program should be able to<br />
calculate the same value for the nuclear repulsion energy, given the same crystal structure. By<br />
default casino computes the Ewald interaction and compares it with the value given in the<br />
wave-function file. If they differ by more than 10 −5 , then casino will stop and complain. If you<br />
have a justifiable reason for doing so (e.g., you have turned <strong>of</strong>f periodicity), you may turn <strong>of</strong>f<br />
this check by setting ewald check to F.<br />
EWALD CONTROL (Real) This is the percentage increase (from the default) <strong>of</strong> the cut<strong>of</strong>f radius<br />
for the reciprocal space sum in the Ewald interaction, which is used for calculating electrostatic<br />
interactions between particles in periodic systems. Its default value is zero. Increasing<br />
ewald control will cause more vectors to be included in the sum, the effect <strong>of</strong> which is to<br />
increase the range <strong>of</strong> the Ewald γ parameter over which the energy is constant (the default<br />
γ should lie somewhere in the middle <strong>of</strong> this range). This need only be done in exceptional<br />
circumstances and the default should be fine for the general user. See Sec. 19.4 for information<br />
about the Ewald method.<br />
EXPOT (Logical) If expot is set to T then an external potential is read from the file expot.data<br />
and included as a summed contribution to the total energy. See Sec. 7.9.<br />
EXPVAL CUTOFF (Physical) expval cut<strong>of</strong>f is the energy cut<strong>of</strong>f for G-vectors used in the evaluation<br />
<strong>of</strong> expectation values accumulated in reciprocal space (e.g., the density, spin density,<br />
pair-correlation function, etc.). The value <strong>of</strong> expval cut<strong>of</strong>f is ignored if an expval.data file is<br />
already present, in which case the G-vector set(s) given therein are used instead. If you set it<br />
to zero, then the program will suggest a value. The default is 3 a.u. See Sec. 7.11.<br />
EXPVAL ERROR BARS (Logical) If this flag is set, casino will, where practicable, accumulate<br />
the additional quantities required to evaluate error bars on requested expectation values. This<br />
will increase the size <strong>of</strong> the expval.data file and slow down the calculation slightly. At present<br />
this functionality is limited to the structure factor.<br />
EXPVAL KGRID (Block) This block contains a specification <strong>of</strong> one or more k-point grids defined in<br />
one, two or three dimensions. A one-dimensional grid is defined by a line AB, a two-dimensional<br />
grid by a plane AB–AC and a three-dimensional grid by a parallelepiped AB–AC–AD, together<br />
with an appropriate number <strong>of</strong> k-points along each direction. These grids may be used in the<br />
calculation <strong>of</strong> various expectation values, if the appropriate keywords are set to T in input. The<br />
block consists <strong>of</strong> the following lines:<br />
Line 1: Number <strong>of</strong> grids defined in this block;<br />
Line 2: Which expectation value uses this grid? (2 for spherical structure factor);<br />
Line 3: Dimensionality d <strong>of</strong> current k-grid (1–3);<br />
Line 4: Coordinates <strong>of</strong> k-point A (a.u.);<br />
Line 5: Coordinates <strong>of</strong> k-point B (a.u.), number <strong>of</strong> points along AB;<br />
Line 6: [If d = 2 or 3] Coordinates <strong>of</strong> k-point C (a.u.), number <strong>of</strong> points along AC;<br />
Line 7: [If d = 3] Coordinates <strong>of</strong> k-point D (a.u.), number <strong>of</strong> points along AD.<br />
Repeat lines 2 to 7 for each additional grid.<br />
Note that spherically averaged quantities require a one-dimensional grid, irrespective <strong>of</strong> the<br />
dimensionality <strong>of</strong> the system.<br />
FINITE SIZE CORR (Logical) Calculate finite-size corrections to the kinetic energy and the<br />
electron–electron interaction energy in periodic systems using the method described in Ref.<br />
[17]. See Secs. 29 and 30 for further information.<br />
FIX HOLES (Logical) This keyword is used to define the reference points for the exciton-exciton<br />
separation when using the ‘BIEX3’ wave function. Setting fix holes to T means that the two<br />
holes are fixed at a distance xx sep apart. The default is F, in which case the centres <strong>of</strong> mass<br />
<strong>of</strong> the two excitons are fixed instead. If BIEX3 is not being used then this keyword is ignored.<br />
FORCES (Logical) Calculate atomic forces in VMC/DMC. Forces are only implemented for Gaussian<br />
basis sets and only work in pseudopotential calculations (in order to eliminate the electron–<br />
nucleus singularity).<br />
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