Chemistry Reference
In-Depth Information
I
II
Figure 13
Smaller domain (region I) represents the part of the system where the detailed
physics is relevant and that is, therefore, described using OFDFT. The larger domain
(region II) is the region described by the atomistic classical potential (usually EAM).
Region I is embedded into region II and is always nonperiodic, while periodic boundary
conditions can be applied to region II.
(the rest of the system) that is simulated using classical potentials (Figure 13).
Because OFDFT is particularly well suited for metallic systems, embedded
atom method (EAM) potentials
9,10
are the preferred choice for the atomistic
potentials.
This methodology adopts the single energy functional strategy, i.e., the
energy of the whole system is written as the sum of the energies of the two
regions (
E
1
and
E
2
), plus a term that describes the interaction energy of these
two regions (the hand-shake term):
E
hand shake
E
½
I
þ
II
¼
E
1
½
I
þ
E
2
½
II
þ
½
I
;
II
;
½
59
where label I indicates quantities evaluated in the smaller, higher resolution
region (where OFDFT is used), and II indicates quantities evaluated in the
larger, lower resolution region (where EAM is used). The energies,
E
1
and
E
2
, are calculated using DFT (or OFDFT) and a classical potential, respec-
tively. The coupling energy, E
hand shake
[I, II], can be computed either way,
which gives rise to two possible coupling schemes.
In the first scheme, E
hand shake
[I, II] is calculated classically. Specifically,
it is obtained as
E
hand shake
½
I
;
II
¼
E
cl
½
I
þ
II
E
cl
½
I
E
cl
½
II
½
60
