[angelofm]

Well in my experience you cannot really get to the same speed of the morning, you have been working for some hours, your brain is tired its only natural to not be as productive in the afternoon.

As another person pointed out what you eat and how long you slept play a key role in making you feel tired.

Every person is different but what works for me it's diving into my little word, basically try to achieve a level of concentration where whatever you are doing feels magical, I put my headphones in and every little code I write I try to appreciate and feel like I am doing some progress, this has the side effect of making me happy and to enjoy what I am doing.