I wrote a blog post on how to burn the Arduino bootloader onto the ATmega328p chips. If anyone is interested, here's the link! I found that a lot of the tutorials out there were incomplete or skipped steps, so I wrote one that takes you through the whole processs. I plan to use these nodes to create an IoT network that operates under the LowPower library and at a lower crystal frequency (4 MHz). I will update as that progresses. Here is the website link and a wiring diagram for the Arduino as ISP:
Arduino Internet of Things Part 1: Burning The Arduino Bootloader Onto A Blank ATmega328p Chip Using The Arduino Uno (https://engineersportal.com/blog/2018/3/15/arduino-internet-of-things-part-1-burning-the-arduino-bootloader-onto-a-blank-atmega328p-chip-using-the-arduino-uno)
You forgot to add 0.1 uF decoupling capacitors on the power inputs of the ATmega328P.
Now, in the Arduino IDE the Programmer needs to be set as 'Arduion as ISP'
Once this is done, one can treat the ATmega on the breadboard as a classic Arduino board.
This seems unnecessarily vague. Why not be specific and say: "one can treat the ATmega on the breadboard as an Arduino Uno."?
An external LED blink sketch is a good sketch to start with, or even an analog read/write sketch to test that the bootloader has been burned correctly.
I think it would be worth mentioning that the physical pins numbers on the ATmega328P used throughout the tutorial are not the Arduino pin numbers. Otherwise the reader is likely to have a bad time at this step when their LED is connected to PD7 but they're blinking PB5.
It's a bad idea to stuff multiple component leads into the same hole on the breadboard because it can stretch out the springs, causing other components later used in that hole to not get a good connection.