Strain groups in database{ …_zb{} } and database{ …_wz{} }¶
Note
This section is under construction
There are about 23 identical groups available directly under all zincblende- and wurtzite-related groups. In this section we describe four of them, specifically all groups related to strain parameters:
lattice_consts{}
elastic_consts{}
piezoelectric_consts{}
pyroelectric_consts{}
(only wurtzite)
Strain for zincblende¶
database{ …{ lattice_consts{} } } for zincblende¶
- a
- type:
double
- unit:
Angstrom
Specify lattice constant at 300K. In a cubic crystal system (like diamond and zincblende), the lattice constants in all three crystal axes are equal.
- a_expansion
- type:
double
- unit:
Angstom/K
The lattice constants are temperature dependent. The lattice constant
a
in the database should be given for 300 K. For all other temperatures, the lattice constant is calculated by the following formula:\[\mathrm{a(T) = a_{300 K} + a\_expansion \cdot (T - 300 K)}\]where T is the temperatue in units of K.
database{ …{ elastic_consts{} } } for zincblade¶
Specify elastic constants:
- c11
- type:
double
- unit:
GPa
- c12
- type:
double
- unit:
GPa
- c44
- type:
double
- unit:
GPa
database{ …{ piezoelectric_consts{} } } for zincblade¶
Specify piezoelectric constants (If strain is present, then generally piezoelectric charges and thus piezoelectric fields arise):
- e14
- type:
double
- unit:
C/m\(^2\)
- B114 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
- B124 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
- B156 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
Note
For silicon and germanium there is no piezoelectric effect at all, thus the constants are zero in this case.
Strain for wurtzite¶
database{ …{ lattice_consts{} } } for wurtzite¶
- a
Lattice constant at 300 K (perpendicular to hexagonal c axis). In a hexagonal crystal system, the two lattice constants perpendicular to the hexagonal c axis are equal.
- type:
double
- unit:
Angstrom
- c
Lattice constant at 300 K (along hexagonal c axis)
- type:
double
- unit:
Angstrom
- a_expansion
- type:
double
- unit:
Angstrom/K
- c_expansion
- type:
double
- unit:
Angstrom/K
The formaula for the temperature dependency of the lattice constants
a
andc
in wurtzite is the same as fora
in zincblende.
database{ …{ elastic_consts{} } } for wurtzite¶
Specify elastic constants:
- c11
- type:
double
- unit:
GPa
- c12
- type:
double
- unit:
GPa
- c13
- type:
double
- unit:
GPa
- c33
- type:
double
- unit:
GPa
- c44
- type:
double
- unit:
GPa
database{ …{ piezoelectric_consts{} } } for wurtzite¶
Specify piezoelectric constants (If strain is present, then generally piezoelectric charges and thus piezoelectric fields arise):
- e31
- type:
double
- unit:
C/m\(^2\)
- e33
- type:
double
- unit:
C/m\(^2\)
- e15
- type:
double
- unit:
C/m\(^2\)
- B311 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
- B312 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
- B313 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
- B333 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
- B115 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
- B125 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
- B135 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
- B344 (optional)
\(\mathrm{2^{nd}}\) order piezoelectric constant
- type:
double
- unit:
C/m\(^2\)
database{ …{ pyroelectric_consts{} } } for wurtzite¶
Specify pyroelectric constants (for spontaneous polarization).
- p1
- type:
double
- unit:
C/m\(^2\)
The pyroelectric field is directed along the hexagonal c axis ([0 0 0 1] direction).