\documentclass[tikz,border=5pt]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{tikz}
\usetikzlibrary{automata, arrows.meta, calc, fit, positioning, shapes, shapes.misc}
\usepackage{amsmath,amssymb}
\definecolor{borderColour}{HTML}{2f528f}
\definecolor{myBlue}{HTML}{4472c4}
\definecolor{myOrange}{HTML}{ed7d31}
\definecolor{myGreen}{HTML}{92d050}
\tikzset{box/.style={
draw=borderColour, very thick,
minimum width=2.5cm,
inner sep=2mm,
align=center,
minimum height=1cm}}
\tikzset{input/.style={
trapezium,
trapezium left angle = 65,
trapezium right angle = 115,
trapezium stretches}}
\tikzset{choice/.style={
diamond,
aspect=2.5}}
\tikzset{connect/.style={->, >=latex, ultra thick, borderColour}}
\begin{document}
\begin{tikzpicture}[font=\small,align=center,node distance=0.75cm]
\definecolor{borderColour}{HTML}{2f528f}
\definecolor{myBlue}{HTML}{4472c4}
\definecolor{myOrange}{HTML}{ed7d31}
\definecolor{myGreen}{HTML}{92d050}
\tikzset{box/.style={
draw=borderColour, very thick,
minimum width=2.5cm,
inner sep=2mm,
align=center,
minimum height=1cm}}
\tikzset{input/.style={
trapezium,
trapezium left angle = 65,
trapezium right angle = 115,
trapezium stretches}}
\tikzset{choice/.style={
diamond,
aspect=2.5}}
\tikzset{connect/.style={->, >=latex, ultra thick, borderColour}}
\node[box,rounded rectangle] (START) at (0, 0) {START};
\node[box,input,below=of START] (Rho0) {DFT SCF: Find self-consistent solution for the \\
normal-state electronic density
$\rho_0$};
\node[box,below=1cm of Rho0] (HofRho) {Construct $h^{\mathrm{KS}}_{\mu\nu}[\rho_0]$};
\node[box,choice,below=1.5cm of HofRho ] (Oneshot) {non SCF-BdG\\ method?};
\node[box,below=1.2cm of Oneshot] (Diag) {Solve eigenvalue problem: \\
$\left(\begin{array}{cc}
h^{KS}_{\mu\nu} & \Delta_{\mu\nu}\\
-\Delta^*_{\mu\nu} & -h^{KS}*_{\mu\nu}
\end{array}\right)
\left(\begin{array}{c}
u_{\nu}\\
v_{\nu}
\end{array} \right)
= \varepsilon \left(\begin{array}{cc}
\mathbf{S}_{\mu\nu} & 0\\
0 & \mathbf{S}_{\mu\nu}
\end{array} \right)
\left(\begin{array}{c}
u_{\nu}\\
v_{\nu}
\end{array} \right)$};
\node[box,below=of Diag] (CalcRhoChiFixD0) {Construct $\rho$ and $\chi$ matrices
from $\left(\begin{array}{c} u_{\nu}\\\\ v_{\nu}\end{array} \right)$};
\node[box,choice,below=of CalcRhoChiFixD0 ] (FixDorFixL) {Fixed-$\Delta$ or \\ full SCF-BdG?};
\node[box,rounded rectangle,left=2cm of FixDorFixL] (FixD) {Fixed-$\Delta$};
\node[box,below=1.2cm of FixD] (CalcHk) {Construct $h^{KS}_{\mu\nu}$};
\node[box,choice,below=of CalcHk ] (SCFixD) {Self-consistent\\
$\rho$ and $h^{KS}_{\mu\nu}$?};
\node[box,rounded rectangle,right=2cm of FixDorFixL] (FixL) {full SCF-BdG};
\node[box,below=1.2cm of FixL] (CalchDFixL) {Construct $h^{KS}_{\mu\nu}$ and $\Delta_{\mu\nu}$};
\node[box,choice,below=of CalchDFixL] (SCFixL) {Self-consistent\\
$\rho$, $h^{KS}_{\mu\nu}$, $\chi$, $\Delta$?};
\node[box,choice,below=5cm of FixDorFixL] (Charge) {Charge conserved?};
\node[box,choice,below=of Charge] (Fermi) {Update Fermi level?};
\node[box,below=1.5cm of Fermi] (Postprocess) {Solve eigenvalue problem: \\
$\left(\begin{array}{cc}
h^{KS}_{\mu\nu} & \Delta_{\mu\nu}\\
-\Delta^*_{\mu\nu} & -h^{KS}*_{\mu\nu}
\end{array}\right)
\left(\begin{array}{c}
u_{\nu}\\
v_{\nu}
\end{array} \right)
= \varepsilon \left(\begin{array}{cc}
\mathbf{S}_{\mu\nu} & 0\\
0 & \mathbf{S}_{\mu\nu}
\end{array} \right)
\left(\begin{array}{c}
u_{\nu}\\
v_{\nu}
\end{array} \right)$ \\
for bands, PDOS, $\chi$, etc.};
\draw[connect] (START) -- (Rho0);
\draw[connect] (Rho0) -- (HofRho);
\draw[connect] (HofRho) -- (Oneshot) node[pos=0.5,fill=white,inner sep=1mm]{Input $\Delta_{\mu\nu}$};
\draw[connect] (Oneshot) -- ++(13cm,0) node[pos=0.5,fill=white,inner sep=1mm]{Yes} |- node[pos=0.25,fill=white,inner sep=1mm]{\textit{skip} \\ \textsc{SIESTA}-BdG\\\textit{SCF loop}} (Postprocess);
\draw[connect] (Oneshot) -- (Diag) node[pos=0.35,fill=white,inner sep=1mm]{No};
\node (SCF) [box,draw=myOrange,rounded corners,inner sep=11mm,fit = (Diag) (SCFixD) (SCFixL)(Fermi),label={[anchor=center,fill=white,font=\large,text=myOrange]135:{\textbf{\textsc{SIESTA}-BdG SCF loop}}},
minimum width=21.3cm] {};
\draw[connect] (Diag) -- (CalcRhoChiFixD0);
\draw[connect] (CalcRhoChiFixD0) -- (FixDorFixL);
\draw[connect] (FixDorFixL) -- (FixD);
\draw[connect] (FixDorFixL) -- (FixL);
\draw[connect] (FixD) -- (CalcHk);
\draw[connect] (CalcHk)-- (SCFixD);
\draw[connect] (SCFixD) -- (Charge) node[pos=0.35,fill=white,inner sep=1mm]{Yes};
\draw[connect] (SCFixD) -- ++ (-3.91cm,0) node[pos=0.5,fill=white,inner sep=1mm]{No} |- (Diag);
\draw[connect] (FixL) -- (CalchDFixL)node[pos=0.5,fill=white,inner sep=1mm]{Input $\lambda$};
\draw[connect] (CalchDFixL) -- (SCFixL);
\draw[connect] (SCFixL) -- (Charge) node[pos=0.35,fill=white,inner sep=1mm]{Yes};
\draw[connect] (SCFixL) -- ++ (4.275cm,0) node[pos=0.5,fill=white,inner sep=1mm]{No} |- (Diag);
\draw[connect] (Charge) -- (Fermi) node[pos=0.35,fill=white,inner sep=1mm]{No};
\draw[connect] (Charge) -- ++(7cm,0) node[pos=0.5,fill=white,inner sep=1mm]{Yes} |- (Postprocess);
\draw[connect] (Fermi) -- ++(-10.250cm,0) node[pos=0.5,fill=white,inner sep=1mm]{Yes} |- (Diag);
\draw[connect] (Fermi) -- (Postprocess) node[pos=0.5,fill=white,inner sep=1mm]{No};
\end{tikzpicture}
\end{document}