Why is bibtex mangaling \v{S} into v?

the multibyte characters fail when bibtex is trying to take "the first letter" and just takes the first byte. Also bibtex's syntax for accent commands is {\v S} not \v{S} so you can use either of these forms:

Ognjen {\relax Š} or Ognjen {\v S}

You are missing a brace, but beside this, add braces around the \v{S}. without it bibtex reads it as a "von":

@Article{LaTeX,
    author ="Chen, Teng-Hao and Lee, Semin and Flood, Amar H. and Miljanić, Ognjen {\v{S}}.",
    title  ="How to print a crystal structure model in 3D",
    journal  ="CrystEngComm",
}