Rework periodic part.

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Marek Nečada 2020-06-22 15:25:55 +03:00
parent eb26821d11
commit 3ce1210d8a
1 changed files with 229 additions and 84 deletions

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@ -1063,11 +1063,28 @@ FP: Check signs.
\begin_inset Formula
\begin{equation}
\sigma_{l,m}\left(\vect k,\vect s\right)=\sum_{\vect n\in\ints^{d}}\left(1-\delta_{\vect{R_{n}},\vect s}\right)e^{i\vect{\vect k}\cdot\left(\vect R_{\vect n}-\vect s\right)}\sswfoutlm lm\left(\vect{R_{n}}-\vect s\right),\label{eq:sigma lattice sums}
\sigma_{l,m}\left(\vect k,\vect s\right)=\sum_{\vect n\in\ints^{d}}\left(1-\delta_{\vect{R_{n}},\vect s}\right)e^{i\vect{\vect k}\cdot\vect R_{\vect n}}\sswfoutlm lm\left(\kappa\left(\vect s+\vect{R_{n}}\right)\right),\label{eq:sigma lattice sums}
\end{equation}
\end_inset
\begin_inset Note Note
status open
\begin_layout Plain Layout
\begin_inset Formula
\begin{equation}
\sigma_{l,m}\left(\vect k,\vect s\right)=\sum_{\vect n\in\ints^{d}}\left(1-\delta_{\vect{R_{n}},\vect s}\right)e^{i\vect{\vect k}\cdot\left(\vect R_{\vect n}-\vect s\right)}\sswfoutlm lm\left(\vect{R_{n}}-\vect s\right),\label{eq:sigma lattice sums-1}
\end{equation}
\end_inset
\end_layout
\end_inset
we see from eqs.
\begin_inset CommandInset ref
@ -1129,6 +1146,10 @@ W_{\alpha,\tau lm;\beta,\tau'l'm'}(\vect k) & =\sum_{\lambda=\left|l-l'\right|+1
\end_inset
\begin_inset Note Note
status open
\begin_layout Plain Layout
\begin_inset Formula
\[
W_{\alpha,\tau lm;\beta,\tau'l'm'}(\vect k)=\sum_{\lambda=\left|l-l'\right|+\left|\tau-\tau'\right|}^{l+l'}\tropcoeff_{\tau lm;\tau'l'm'}^{\lambda}\sigma_{\lambda,m-m'}\left(\vect k,\vect r_{\beta}-\vect r_{\alpha}\right),\quad\tau'\ne\tau,
@ -1137,6 +1158,19 @@ W_{\alpha,\tau lm;\beta,\tau'l'm'}(\vect k)=\sum_{\lambda=\left|l-l'\right|+\lef
\end_inset
\end_layout
\end_inset
\begin_inset Formula
\[
W_{\alpha,\tau lm;\beta,\tau'l'm'}(\vect k)=\sum_{\lambda=\left|l-l'\right|+\left|\tau-\tau'\right|}^{l+l'}\tropcoeff_{\tau lm;\tau'l'm'}^{\lambda}\sigma_{\lambda,m-m'}\left(-\vect k,\vect r_{\alpha}-\vect r_{\beta}\right),\quad\tau'\ne\tau,
\]
\end_inset
\begin_inset Note Note
status open
@ -1223,13 +1257,18 @@ FP: Check sign of s
\begin_layout Standard
\begin_inset Formula
\begin{multline}
\sigma_{l,m}^{\left(\mathrm{S},\eta\right)}\left(\vect k,\vect s\right)=-\frac{2^{l+1}i}{\kappa^{l+1}\sqrt{\pi}}\sum_{\vect n\in\ints^{d}}\left(1-\delta_{\vect{R_{n}},-\vect s}\right)\left|\vect{R_{n}+\vect s}\right|^{l}\ush lm\left(\vect{R_{n}+\vect s}\right)e^{i\vect k\cdot\left(\vect{R_{n}+\vect s}\right)}\\
\times\int_{\eta}^{\infty}e^{-\left|\vect{R_{n}+\vect s}\right|^{2}\xi^{2}}e^{-\kappa^{2}/4\xi^{2}}\xi^{2l}\ud\xi\\
+\delta_{\vect{R_{n}},-\vect s}\frac{\delta_{l0}\delta_{m0}}{\sqrt{4\pi}}\Gamma\left(-\frac{1}{2},-\frac{\kappa^{2}}{4\eta^{2}}\right)\ush lm\left(\vect{R_{n}+\vect s}\right).\label{eq:Ewald in 3D short-range part}
\sigma_{l,m}^{\left(\mathrm{S},\eta\right)}\left(\vect k,\vect s\right)=-\frac{2^{l+1}i}{\kappa^{l+1}\sqrt{\pi}}\sum_{\vect n\in\ints^{d}}\left(1-\delta_{\vect{R_{n}},-\vect s}\right)\left|\vect s_{\vect n}\right|^{l}\ush lm\left(\uvec s_{\vect n}\right)e^{i\vect k\cdot\vect{R_{n}}}\\
\times\int_{\eta}^{\infty}e^{-\left|\vect s_{\vect n}\right|^{2}\xi^{2}}e^{-\kappa^{2}/4\xi^{2}}\xi^{2l}\ud\xi\\
+\delta_{\vect{R_{n}},-\vect s}\frac{\delta_{l0}\delta_{m0}}{\sqrt{4\pi}}\Gamma\left(-\frac{1}{2},-\frac{\kappa^{2}}{4\eta^{2}}\right)\ush lm\left(\uvec s_{\vect n}\right),\label{eq:Ewald in 3D short-range part}
\end{multline}
\end_inset
where we labeled
\begin_inset Formula $\vect s_{\vect n}\equiv\vect s+\vect R_{\vect n}$
\end_inset
.
The formal
\begin_inset Formula $\left(1-\delta_{\vect{R_{n}},-\vect s}\right)$
\end_inset
@ -1355,7 +1394,19 @@ The explicit form of the long-range part of the lattice sum depends on the
\end_inset
.
In the following, let us label
\begin_inset Formula $\vect k_{\vect K}\equiv\vect k+\vect K$
\end_inset
, where
\begin_inset Formula $\vect K$
\end_inset
is a point in the reciprocal lattice, and let
\begin_inset Formula $\mathcal{A}$
\end_inset
be the lattice unit cell volume (or area/length in the 2D/1D cases).
\end_layout
\begin_layout Paragraph
@ -1369,7 +1420,7 @@ Case
\begin_layout Standard
\begin_inset Formula
\begin{equation}
\sigma_{l,m}^{\left(\mathrm{L},\eta\right)}\left(\vect k,\vect s\right)=\frac{4\pi i^{l+1}}{\kappa\mathcal{A}}\sum_{\vect K\in\Lambda^{*}}\underbrace{e^{i\vect K\cdot\vect s}}_{\text{nemá tu být \ensuremath{\vect{k\cdot s}?}}}\frac{\left(\left|\vect k+\vect K\right|/\kappa\right)^{l}}{\kappa^{2}-\left|\vect k+\vect K\right|^{2}}e^{\left(\kappa^{2}-\left|\vect k+\vect K\right|^{2}\right)/4\eta^{2}}\ush lm\left(\vect k+\vect K\right)\label{eq:Ewald in 3D long-range part 3D}
\sigma_{l,m}^{\left(\mathrm{L},\eta\right)}\left(\vect k,\vect s\right)=\frac{4\pi i^{l+1}}{\kappa\mathcal{A}}\sum_{\vect K\in\Lambda^{*}}e^{-i\vect k_{\vect K}\cdot\vect s}\frac{\left(\left|\vect k_{\vect K}\right|/\kappa\right)^{l}}{\kappa^{2}-\left|\vect k_{\vect K}\right|^{2}}e^{\left(\kappa^{2}-\left|\vect k_{\vect K}\right|^{2}\right)/4\eta^{2}}\ush lm\left(\uvec k_{\vect K}\right)\label{eq:Ewald in 3D long-range part 3D}
\end{equation}
\end_inset
@ -1384,14 +1435,115 @@ regardless of chosen coordinate axes.
\end_layout
\begin_layout Paragraph
Case
\begin_inset Formula $d=2$
Cases
\begin_inset Formula $d=1,2$
\end_inset
\end_layout
\begin_layout Standard
In the quasiperiodic cases, we decompose vectors into parallel and orthogonal
parts with respect to the linear subspace in which the Bravais lattice
lies (the reciprocal lattice lies in the same subspace),
\begin_inset Formula $\vect v=\vect v_{\perp}+\vect v_{\parallel}$
\end_inset
, and we label
\begin_inset Formula
\begin{equation}
\gamma_{\vect k_{\vect K}}\equiv\gamma_{\vect k_{\vect K}}\left(\kappa\right)\equiv\left(\left|\vect k_{\vect K}\right|^{2}-\kappa^{2}\right)^{\frac{1}{2}}/\kappa,\label{eq:lilgamma}
\end{equation}
\end_inset
\begin_inset Formula
\begin{equation}
\Delta_{d;j}\left(x,z\right)\equiv\int_{x}^{\infty}t^{-\frac{d_{c}}{2}-n}\exp\left(-t+\frac{z^{2}}{4t}\right)\ud t,\label{eq:Delta_j}
\end{equation}
\end_inset
where
\begin_inset Formula $d_{c}=3-d$
\end_inset
is the complementary dimension of the lattice.
Then
\begin_inset Formula
\begin{multline}
\sigma_{l}^{m}\left(\vect k,\vect s\right)=\frac{-i}{2\pi^{d_{c}/2}\mathcal{A}\kappa}\frac{\left(2l+1\right)!!}{\kappa^{l}}\sum_{\vect K\in\Lambda^{*}}e^{-i\vect k_{\vect K}\cdot\vect s}\times\\
\times\sum_{j=0}^{l}\frac{\left(-1\right)^{j}}{j!}\left(\frac{\kappa\gamma_{\vect k_{\vect K}}}{2}\right)^{2j}\Delta_{d;j}\left(\frac{\kappa^{2}\gamma_{\vect k_{\vect K}}^{2}}{4\eta^{2}},-i\kappa\gamma_{\vect k_{\vect K}}\left|\vect s_{\perp}\right|\right)\times\\
\times\sum_{l'=\max\left(0,l-2j\right)}^{l-j}4\pi i^{l'}\left(2\left|\vect s_{\bot}\right|\right)^{2j-l+l'}\frac{\left|\vect k_{\vect K}\right|^{l'}}{\left(2l'+1\right)!!}\sum_{m'=-l'}^{l'}\ush{l'}{m'}\left(\uvec k_{\vect K}\right)\times\\
\times\int\ud\Omega_{\vect r}\,\ush lm\left(\uvec r\right)\ushD{l'}{m'}\left(\uvec r\right)\left(\frac{\left|\vect r_{\perp}\right|}{\left|\vect r\right|}\right)^{l-l}\left(\frac{-\vect r_{\perp}\cdot\vect s_{\perp}}{\left|\vect r_{\perp}\right|\left|\vect s_{\perp}\right|}\right)^{2j-l+l'}.\label{eq:Ewald in 3D long-range part 1D 2D}
\end{multline}
\end_inset
The angular integral on the last line of
\begin_inset CommandInset ref
LatexCommand eqref
reference "eq:Ewald in 3D long-range part 1D 2D"
plural "false"
caps "false"
noprefix "false"
\end_inset
gives a set of constant coefficients characteristic to a chosen convention
for spherical harmonics and coordinate axes; relatively simple closed-form
expressions are obtained for 2D periodicity if we choose the lattice to
lie in the
\begin_inset Formula $xy$
\end_inset
plane, so that both
\begin_inset Formula $\vect r_{\perp},\vect s_{\perp}$
\end_inset
are parallel to the
\begin_inset Formula $z$
\end_inset
axis, as done in
\begin_inset CommandInset citation
LatexCommand cite
key "kambe_theory_1968"
literal "false"
\end_inset
, see also Supplementary Material.
In the special case
\begin_inset Formula $\vect s_{\perp}=0$
\end_inset
the expressions can be considerably simplified as most of the terms vanish
and
\begin_inset Formula $\Delta_{d;j}\left(x,0\right)=\Gamma\left(1-d_{c}/2-j,x\right)$
\end_inset
, but the general case is needed for evaluating the fields in space (see
Section
\begin_inset CommandInset ref
LatexCommand ref
reference "subsec:Periodic scattering and fields"
plural "false"
caps "false"
noprefix "false"
\end_inset
) or if there is an offset between two particles in a unitcell that is not
parallel to the lattice subspace.
\end_layout
\begin_layout Standard
\begin_inset Note Note
status open
\begin_layout Plain Layout
Reasonable explicit forms assume that the lattice lies inside the
\begin_inset Formula $xy$
\end_inset
@ -1462,12 +1614,17 @@ FP: check sign of
j\le s\le\min\left(2j,l-\left|m\right|\right)\\
l-n+\left|m\right|\,\mathrm{even}
}
}\frac{1}{\left(2j-s\right)!\left(s-j\right)!}\frac{\left(-\kappa s_{\perp}\right)^{2j-s}\left(\left|\vect k+\vect K\right|/\kappa\right)^{l-s}}{\left(\frac{1}{2}\left(l-m-s\right)\right)!\left(\frac{1}{2}\left(l+m-s\right)\right)!}\label{eq:Ewald in 3D long-range part 1D 2D}
}\frac{1}{\left(2j-s\right)!\left(s-j\right)!}\frac{\left(-\kappa s_{\perp}\right)^{2j-s}\left(\left|\vect k+\vect K\right|/\kappa\right)^{l-s}}{\left(\frac{1}{2}\left(l-m-s\right)\right)!\left(\frac{1}{2}\left(l+m-s\right)\right)!}\label{eq:Ewald in 3D long-range part 1D 2D-1}
\end{multline}
\end_inset
\end_layout
\end_inset
\begin_inset Note Note
status open
@ -1486,23 +1643,12 @@ status open
\end_inset
where
\begin_inset Formula
\begin{equation}
\gamma\left(z\right)=\left(z^{2}-1\right)^{\frac{1}{2}},\label{eq:lilgamma}
\end{equation}
\end_inset
\begin_inset Note Note
status open
\begin_inset Formula
\begin{equation}
\Delta_{j}\left(x,z\right)=\int_{x}^{\infty}t^{\frac{-1}{2}-n}\exp\left(-t+\frac{z^{2}}{4t}\right)\ud t.\label{eq:Delta_j}
\end{equation}
\end_inset
If the normal component
\begin_layout Plain Layout
where If the normal component
\begin_inset Formula $s_{\bot}$
\end_inset
@ -1538,12 +1684,20 @@ noprefix "false"
\end_inset
.
\end_layout
\end_inset
\end_layout
\begin_layout Standard
If
\begin_inset Formula $s_{\bot}\ne0$
\end_inset
, the integral
\begin_inset Formula $\Delta_{j}\left(x,z\right)$
\begin_inset Formula $\Delta_{d;j}\left(x,0\right)$
\end_inset
can be evaluated e.g.
@ -1555,7 +1709,7 @@ using the Taylor series
\begin_inset Formula
\[
\Delta_{j}\left(x,z\right)=\sum_{k=0}^{\infty}\Gamma\left(\frac{1}{2}-j-k,x\right)\frac{\left(z/2\right)^{2k}}{k!}
\Delta_{d;j}\left(x,z\right)=\sum_{k=0}^{\infty}\Gamma\left(1-\frac{d_{c}}{2}-j-k,x\right)\frac{\left(z/2\right)^{2k}}{k!}
\]
\end_inset
@ -1586,27 +1740,19 @@ noprefix "false"
\end_inset
by parts (note that the signs are wrong in
\begin_inset CommandInset citation
LatexCommand cite
key "kambe_theory_1968"
literal "false"
\end_inset
)
by parts (with signs corrected here):
\begin_inset Formula
\begin{equation}
\Delta_{j+1}\left(x,z\right)=\frac{4}{z^{2}}\left(\left(\frac{1}{2}-j\right)\Delta_{j}\left(x,z\right)-\Delta_{j-1}\left(x,z\right)+x^{\frac{1}{2}-j}e^{-x+\frac{z^{2}}{4x}}\right)\label{eq:Delta_j recurrent}
\Delta_{d;j+1}\left(x,z\right)=\frac{4}{z^{2}}\left(\left(\frac{1}{2}-j\right)\Delta_{d;j}\left(x,z\right)-\Delta_{d;j-1}\left(x,z\right)+x^{\frac{d_{c}}{2}-j}e^{-x+\frac{z^{2}}{4x}}\right)\label{eq:Delta_j recurrent}
\end{equation}
\end_inset
with the first two terms
with the first two terms for 2D periodicity
\begin_inset Formula
\begin{align*}
\Delta_{0}\left(x,z\right) & =\frac{\sqrt{\pi}}{2}e^{-x^{2}+\frac{z^{2}}{4x}}\left(w\left(-\frac{z}{2\sqrt{x}}+i\sqrt{x}\right)+w\left(\frac{z}{2\sqrt{x}}+i\sqrt{x}\right)\right),\\
\Delta_{1}\left(x,z\right) & =i\frac{\sqrt{\pi}}{z}e^{-x^{2}+\frac{z^{2}}{4x}}\left(w\left(-\frac{z}{2\sqrt{x}}+i\sqrt{x}\right)-w\left(\frac{z}{2\sqrt{x}}+i\sqrt{x}\right)\right),
\Delta_{2;0}\left(x,z\right) & =\frac{\sqrt{\pi}}{2}e^{-x^{2}+\frac{z^{2}}{4x}}\left(w\left(-\frac{z}{2\sqrt{x}}+i\sqrt{x}\right)+w\left(\frac{z}{2\sqrt{x}}+i\sqrt{x}\right)\right),\\
\Delta_{2;1}\left(x,z\right) & =i\frac{\sqrt{\pi}}{z}e^{-x^{2}+\frac{z^{2}}{4x}}\left(w\left(-\frac{z}{2\sqrt{x}}+i\sqrt{x}\right)-w\left(\frac{z}{2\sqrt{x}}+i\sqrt{x}\right)\right),
\end{align*}
\end_inset
@ -1717,9 +1863,8 @@ FP: I have some error estimates derived in my notes.
\end_layout
\begin_layout Standard
One pecularity of the two-dimensional case is the two-branchedness of the
function
\begin_inset Formula $\gamma\left(z\right)$
One pecularity of the two-dimensional case is the two-branchedness of
\begin_inset Formula $\gamma_{\vect k_{\vect K}}\left(\kappa\right)$
\end_inset
and the incomplete
@ -1735,7 +1880,7 @@ One pecularity of the two-dimensional case is the two-branchedness of the
\end_inset
the function
\begin_inset Formula $\gamma\left(z\right)$
\begin_inset Formula $\gamma_{\vect k_{\vect K}}\left(\kappa\right)$
\end_inset
appears with even powers, and
@ -1899,21 +2044,6 @@ Detailed physical interpretation of the remaining branch cuts is an open
\end_inset
\begin_inset Note Note
status open
\begin_layout Plain Layout
Generally, a good choice for
\begin_inset Formula $\eta$
\end_inset
is TODO; in order to achieve accuracy TODO, one has to evaluate the terms
on TODO lattice points.
\end_layout
\end_inset
\begin_inset Note Note
status open
@ -1927,23 +2057,6 @@ status open
\end_layout
\begin_layout Paragraph
Case
\begin_inset Formula $d=1$
\end_inset
\end_layout
\begin_layout Standard
For one-dimensional chains, the easiest choice is to align the lattice with
the
\begin_inset Formula $z$
\end_inset
axis.
\end_layout
\begin_layout Subsubsection
Choice of Ewald parameter and high-frequency breakdown
\end_layout
@ -2016,6 +2129,9 @@ Whatabout different geometries?
However, in floating point arithmetics, the magnitude of the summands must
be taken into account as well in order to maintain accuracy.
\end_layout
\begin_layout Standard
There is a particular problem with the
\begin_inset Quotes eld
\end_inset
@ -2026,7 +2142,7 @@ central
reciprocal lattice points in the long-range sums for which the real part
of
\begin_inset Formula $\left|\vect k+\vect K\right|^{2}-\kappa^{2}$
\begin_inset Formula $\left|\vect k_{\vect K}\right|^{2}-\kappa^{2}$
\end_inset
is negative: the incomplete
@ -2077,7 +2193,7 @@ central
\end_inset
needs to be adjusted in a way that keeps the value of
\begin_inset Formula $\Gamma\left(a,\frac{\left|\vect k+\vect K\right|^{2}-\kappa^{2}}{4\eta^{2}}\right)$
\begin_inset Formula $\Gamma\left(a,\left(\left|\vect k_{\vect K}\right|^{2}-\kappa^{2}\right)/4\eta^{2}\right)$
\end_inset
within reasonable bounds.
@ -2197,6 +2313,13 @@ left out for the time being
\begin_layout Subsection
Scattering cross sections and field intensities in periodic system
\begin_inset CommandInset label
LatexCommand label
name "subsec:Periodic scattering and fields"
\end_inset
\end_layout
\begin_layout Standard
@ -2391,14 +2514,36 @@ TODO fix signs and exponential phase factors
\begin_inset Formula
\begin{align*}
\vect E_{\mathrm{scat}}\left(\vect r\right) & =\sum_{\left(\vect n,\alpha\right)\in\mathcal{P}}\sum_{\tau lm}\outcoeffptlm{\vect n,\alpha}{\tau}lm\vect u_{\tau lm}\left(\kappa\left(\vect r-\text{\vect R_{\vect n}-\vect r_{\alpha}}\right)\right)\\
& =\sum_{\alpha\in\mathcal{P}_{1}}e^{-i\vect k\cdot\left(\vect r-\vect r_{\alpha}\right)}\sum_{\tau lm}\outcoeffptlm{\vect 0,\alpha}{\tau}lm\sum_{m'=-1}^{1}\sum_{\lambda=\left|l-1\right|+\left|\tau-2\right|}^{l+1}\tropcoeff_{\tau lm;21m'}^{\lambda}\sigma_{\lambda,m-m'}\left(\vect k,\vect r-\vect r_{\alpha}\right).
\end{align*}
\begin{align}
\vect E_{\mathrm{scat}}\left(\vect r\right) & =\sum_{\left(\vect n,\alpha\right)\in\mathcal{P}}\sum_{\tau lm}\outcoeffptlm{\vect n,\alpha}{\tau}lm\vect u_{\tau lm}\left(\kappa\left(\vect r-\text{\vect R_{\vect n}-\vect r_{\alpha}}\right)\right)\nonumber \\
& =\sum_{\alpha\in\mathcal{P}_{1}}\sum_{\tau lm}\outcoeffptlm{\vect 0,\alpha}{\tau}lm\sum_{m'=-1}^{1}\vswfrtlm 21{m'}\left(0\right)\sum_{\lambda=\left|l-1\right|+\left|\tau-2\right|}^{l+1}\tropcoeff_{\tau lm;21m'}^{\lambda}\sigma_{\lambda,m-m'}\left(-\vect k,\vect r-\vect r_{\alpha}\right).\label{eq:Scattered fields in periodic systems}
\end{align}
\end_inset
In the scattering problem, the total field intensity is obtained by adding
the incident field to
\begin_inset CommandInset ref
LatexCommand eqref
reference "eq:Scattered fields in periodic systems"
plural "false"
caps "false"
noprefix "false"
\end_inset
; whereas in the lattice mode problem the total field is directly given
by
\begin_inset CommandInset ref
LatexCommand eqref
reference "eq:Scattered fields in periodic systems"
plural "false"
caps "false"
noprefix "false"
\end_inset
.
\end_layout
\end_body